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Building A Combination Cabbing Unit
an article in 3 parts
Introduction
Welcome once again to the Low Budget Lapidary, a monthly column of ideas to help you build up your lapidary shop with a minimum of waste and a maximum of ingenuity and common sense. Our focus this month, as last month, is on an essential piece of
equipment for most lapidary hobbyists. Although I am describing a cabbing unit that I built myself, I want to emphasize that this do-it-yourself project is not for everyone! This cabbing unit is a very do-able project for a handy-person who enjoys the
satisfaction of using home-built machines and would rather spend time and save money than the other way around. The majority of lapidary hobbyists (and professionals, for that matter) will be well served by purchasing one of the excellent units on the
market, which exist in almost every price range. My hope is that even the hobbyist who does not want to build a cabbing unit will benefit from this article by gaining a better understanding of how cabbing units work, which will in turn permit you to get
maximum benefit from your machine, to feel more confident when using, troubleshooting, and talking about your machine, and perhaps also to make you a more informed consumer when you go through the process of deciding which unit on the market to
buy.
Last month in this column, I explained how I built an inexpensive and functional rock tumbler. The rock tumbler is an ideal first project for the lapidary shop, because the mechanical principles are fairly simple, and the consequences of error are
not too great. Sure, one could probably manage to kill oneself with a faulty tumbler, through electrocution perhaps, but the odds are small. The most likely consequence of an error in the building of a rock tumbler is a batch of badly tumbled
rocks.
Safety is a more critical issue in our next project, which is a combination cabbing unit. Because the shaft of a cabbing unit turns at a very high rate of speed, there is significant danger to the operator should apparel become tangled in the shaft
or should anything fly off of the shaft to strike the operator. Most commercial cabbing units are designed to minimize these dangers. It is essential that anyone building a home-made cabbing unit must be aware of the potential for danger, and design
accordingly.
This article is the first of a three-part series explaining how I designed and built one such cabbing unit. Because I am an amateur lapidary and not a professional engineer I can make no warranties as to the safety of this design. Please use your
own best judgement if you decide to build your own cabbing unit, and feel free to borrow from my plans that which is helpful to you. In this first article I will provide background concepts and terminology that are common to the wide variety of cabbing
unit designs available. In the second article I will show how my initial design was constructed, along with lessons I learned from cabbing on the unit in that original form. I called the first design "Leviathan I" because it was so huge and so wet to
operate. The third article will explain how I redesigned the cabbing unit, which features an improved shielding design for better visibility and drier operation, and an improved irrigation system for wetting the wheels. The "Leviathan II" is still huge,
but it is easy to use, easily upgradeable, and makes lovely cabs!
Part I: Concepts and terminology
WHAT IS CABBING?
In order to design and build a cabbing unit, we must first understand what it does and how it does it. Allow me to begin, then, by giving an overview of the process of making a cabochon.
"Cabbing" is the art of making a cabochon (or "cab"), which is a lapidary work that features a rounded and polished top. A cabochon is only one of the forms that a lapidary may convert rough rocks or minerals into through some lapidary process.
Other lapidary art forms include tumbling, which is more basic than cabbing and requires less hands-on skill (though getting the proper tumbling action is an art form in itself), and faceting, which requires more specialized equipment and is arguably
more complex (although a well-shaped and polished cabochon may reflect more skill than a poorly faceted gem).
In order to produce a cab, a lapidary first decides upon the material to use. Agates and chalcedonies are hard and well-behaved stones, not too expensive, and well suited to learning to cab. Beginners should probably avoid material that is pitted or
porous, overly soft (like calcite), of varying hardness (like malachite). overly hard (like sapphire), or heavily fractured. Such materials pose their own challenges to the lapidary, and can be mastered in time when the basic techniques have been
mastered.
Before cabbing, the material should be slabbed. You can purchase pre-slabbed material at rock shows, or ask a saw-owning friend to slab your material for you. You can even sometimes purchase a "preform," which is a portion of a slab already trimmed
to the proper approximate shape and size of an intended cab.
If you don't have a preform, you will need to trace the shape of your desired cab onto the stone, trying to capture the prettiest pattern or scene in the stone. There are plastic or metal templates to help you stencil uniform oval or round shapes, or
you can draw a freeform cab onto the stone. If you draw a freeform shape, try to keep all your sides and curves convex (bending outward instead of inward). It will be fairly easy to cab around convex outlines, and much more difficult to cab concave ones.
A sharpened aluminum or brass rod called a scribing pencil leaves a mark that won't wash off during sawing or grinding, and is easy to see.
Now you need to use a trim saw or tile nippers to cut around the shape you've drawn on your slab. You are producing your own preform. Leave 1/8" around the outlines you drew for your cab. You will grind to those outlines later.
GRINDING STAGE
At this point you are ready to cab. You will turn on your grinding unit, adjust your water supply, and use your coarsest grit wheel to grind your preform almost to the line you scribed, holding the preform in your hand and turning it to grind all the
edges on the coarse wheel. Leave a uniform but very small margin around the outline of your cab, well less than half a mm, to ensure that subsequent grinding operations will not leave you with an undersized cab. When the outline is uniform, you will next
grind the edges at a 10-20 degree angle to the top surface of the cab. This is the first step in producing the dome shape. When all sides are uniformly sloped toward the top surface, grind a much smaller chamfer off the edges around the back surface at a
45 degree angle. This will prevent a thin bottom edge to the bottom of the stone, which would tend to chip when you set the stone. Perform the chamfering on the coarse wheel, and then smooth the edges on the fine grinding wheel.
It is very important to thoroughly wash the stone between each grit change -- before fine grinding, and then before each sanding and polishing stage. The stone should be washed with a paste of laundry detergent and water and thoroughly rinsed -- an
old toothbrush is good for this purpose. Don't forget to wash your hands, too. Even a single grain of a coarser grit can gouge the surface of your stone and force you to go all the way back to the coarse grind and start over. This I know from
experience!
Water is needed to flush material from the grinding surfaces, to prevent their being clogged with the material they remove, which would impair their cutting action. A water drip or spray onto the surface of the wheel is typical. Another important
function of water is to keep rock dust from being inhaled. The long-term breathing of silica dust (released by the grinding of silicon bearing rocks including agates and jaspers) is implicated in the formation of silicosis, a potentially fatal lung
disease. Some lapidary materials, for example malachite and some sea shells, also release toxic vapors which water helps to minimize. A prudent lapidary will ensure that ventilation around the cabbing unit is very adequate, and may consider using a
breathing mask rated for removal of airborne particles and vapors (the paper painter's masks don't cut it).
Now you will "dop" the cab, meaning you will attach the back of the cab to a dowel or handle (called a dopstick) using a special lapidary wax (or even superglue). The handle will permit you much more easily to produce a uniform dome and attractive
finish to all parts of the cab's surface (and save your finger tips, which can get pretty cut up if you cab freehand).
When the stone is dopped, it is held a varying angles and revolved against first the coarse and then the fine grinding wheels to create a domed shape. The domed shape evolves much like a topographic map of a uniform hill is drawn -- first the stone
is revolved around one angle to produce one topographic elevation, then it is shifted to another slightly different angle and another level is produced. If you proceed in this way you will produce a nice, uniform dome on the coarse wheel, smooth the
outline further on the fine wheel, and be ready to proceed to the sanding stages.
SANDING STAGE
Grinding surfaces present a hard surface to change the contour of your stone by aggressively removing material. In contrast, sanding surfaces present a more yielding surface to the stone. By permitting the abrasive surface to conform somewhat to
the contour of the stone, a sanding surface tends to round out irregularities in the surface. Even when the abrasive grit size of a sanding surface is larger than that of the fine grinding stage, the action will tend to smooth and round the stone. The
grit size will simply determine the aggressiveness of the smoothing action, as well as the size of the scratches that the action will leave on the stone for removal in subsequent sanding stages. Water must be used in the sanding stage as well, for most
sanding surfaces. [One exception is phenolic spool polishers, which are supposed to operate dry. Dry sanding produces heat which is dissipated in a wet operation, and that heat can be problematic for some stones such as opal.]
In each sanding stage, also referred to as smoothing stages, a finer grade of abrasive grit is used. The stone, dopped to its handle, is pushed into the slightly yielding sanding surface and revolved so that all areas of the surface are uniformly
sanded. The stone is washed and rinsed between each stage to remove any residual particles from the previous stage that could produce scratches and ruin the fineness of the next sanding level.
Different lapidaries may prefer different grit sizes based on their experience with the materials they use. In general, a grit progression of something like 220 or 280, 600, 1200, and 14,000 grit surfaces is used to take a cab from the coarsest
sanding to the finest sanding (or pre-polish) stage. The grits and surfaces used depend very much on the type of sanding material and surface used. The grits stated are very common for lapidaries using diamond sanding wheels or belts, for example.
Lapidaries who use silicon carbide might use a new 220 or 280 belt, then a new 600 grit belt, then an old (worn) 600 grit belt to produce much the same result.
When the stone surface is ready for a polish, after the final sanding stage (or pre-polish stage), it should have a very smooth surface, with no visible scratches. When the only thing missing is the "gloss" finish, the cab is ready for the polish
stage.
POLISHING STAGE
There are several theories as to what physical process actually produces the glossy reflective surface of a good polish; we won't address any of them here. The mechanics of producing a polish generally involve pressing the stone into a somewhat soft
surface (leather, felt, or a specially prepared pad) that has been charged with one of many available polishing compounds. These may be a very fine (50,000 or 100,000 grit) diamond powder or one of many available compounds including cerium oxide, Linda
A, and aluminum oxide, all of which have their fans for certain stones.
If the stone has been properly prepared through a thorough sanding process, then an excellent polish should appear very quickly on most stones.
FINISHING UP
The polished stone should be removed from the handle by heating the stone on a hot metal surface so that the wax softens and the stone may be removed. A soaking in alcohol will remove the residual wax without damaging the polish. If superglue was
used to dop the stone, then an appropriate solvent must be used to remove it, according to the directions for the glue.
Some lapidaries prefer a polished back to the cab, in which case the stone may be dopped on the top, and the back brought through the sanding and polishing stages just as the front was.
SO WHAT IS A CABBING UNIT?
From the description above of the cabbing process, we can see that a "cabbing unit" should have some means of grinding, sanding, and polishing the stones. Some combo units on the market also include a trim saw, but I will not include that feature in
my discussion, as I decided early on that I preferred a separate sawing station. Sawing can be messier than cabbing. I planned to do my cabbing inside my house, and my sawing in the garage.
There is a tremendous variety of cabbing units for sale to today's lapidary, with something in almost every price range. As I planned my own lapidary shop, I found a lot of conflicting information as to what I actually needed, and what the pros and
cons of each design were. At this point, let's examine some of the common types of cabbing units, and determine their strengths and weaknesses.
Multiple accessories mounted, or one at a time?
The process of cabbing requires several types of accessories, and a variety of each type. One or two grinding surfaces, several sanding surfaces, and at least one polishing surface is needed. Some machines provide a single mounting point upon which
the operator fixes the appropriate surface when it is called for. One example of this type of machine is the Cabmate by Graves (list just over $600, including diamond accessories), a handsome and compact unit where the operator changes grinding and
sanding wheels as needed. That unit includes a diamond saw blade for added versatility. A different type of machine that uses interchangeable accessories mounted one at a time is typified by the CrystalMaster 6 by Crystallite. This is probably one of
the least expensive ways to set up for cabbing, at a list of $277 including diamond accessories. These machines both relatively inexpensive and quite compact, but not particularly convenient. After all, only a couple of minutes might be required at
each step of the cabbing process, but these units require a change of accessories before the next step can begin.
Some larger and more expensive machines permit multiple accessories to be mounted at the same time. An example of this type of machine is the Diamond Pacific Genie, which has two grinding wheels and four sanding wheels mounted at all times, with a
polishing disk that easily spins onto threads at one end when needed. Another example of this type of machine is the Cab Pro by Contempo Lapidary, which features one grinding wheel, five sanding belts on drums, and a polishing disk. Each of these
machines retails for under $1500, and features all diamond accessories and integrated irrigation system. On a machine like this, one may proceed from one cabbing stage to the next very easily, pausing only to wash grit from the cab between steps. The
machine does require somewhat more space, however, and is significantly more expensive.
Since I tend to become engrossed in my work and resent having to stop to change accessories, I decided to design a unit that would permit me to mount multiple wheels simultaneously, as the Contempo and Diamond Pacific units do.
Peripheral wheel or flat disk?
Another choice to consider is whether units use peripheral wheels, where the grinding action takes place on the outer circumference of the turning wheel, or flat disks, where the grinding action takes place on the side surface of the disk, between
the central axis and the outer edge. Note that when using a flat disk the speed of the cutting action varies with the distance from the center of the disk -- some consider this a plus, and others can't stand it. I was even told that machines that use
the flat disks for grinding were fine for grinding and polishing flat surfaces like the back of cabs, but were not suitable for the rounded tops of cabs. Since then I have met several people who do all their cabbing on machines just like the
CrystalMaster 6.
There is a type of machine called a "slant cabber", which resembles the flat disk machines in that there is one disk mounted at a time, mounted parallel to a flat face of the machine which is slanted approximately 30 degrees from the horizontal
plane. Though this looks like a flat disk machine, it accepts peripheral disks, and there is room within the wheel well to hold a dopped cab against the periphery of the wheel. A flat disk or a saw blade may also be mounted on this type of machine,
making it a versatile and relatively economical choice (6" units of this type with one diamond wheel, a diamond saw blade, and polishing disk retail for around $500).
Some units employ a peripheral wheel for cabbing, but use flat disks for sanding as well as polishing. This is the case with the Graves Cabmate or the Contempo Multi Flex, which also permit mounting of saw blades and even carving tools.
Diamond or silicon carbide?
If saving money is your primary object, then cabbing can be performed quite inexpensively if you choose silicon carbide rather than diamond accessories. Nevertheless, few lapidaries recommend that choice. Diamond accessories cost significantly
more; a 6" diamond peripheral grinding wheel may cost as much as $200, while a comparable silicon carbide wheel will run less than $30.
Cost is only one consideration, however. Diamond accessories have a much faster cutting action, so that all stages of the cabbing process may be accomplished much faster with diamond than with silicon carbide. This is particularly significant when
cabbing hard materials like agates.
Silicon carbide wheels have a few additional drawbacks, as well. For one thing, there is a danger that they may fly apart at full speed, throwing dangerous projectiles into the operator's face. It is extremely important never to exceed the
manufacturer's recommended speed for any wheel; with silicon carbide, however, there is a significant risk of breakage at excess speeds. Strong shielding is an important safety element in a cabbing unit that uses silicon carbide grinding wheels. Another
drawback of silicon carbide grinding wheels is that they wear away in grooves where you press your stone into them. This produces a great deal of loose grit in your drain water, and care must be taken not to spray water contaminated with coarse grit onto
accessories of a finer grit size. Also, the grooves in the silicon carbide wheel must be frequently dressed out with a dressing bar. In essence, this means that the operator must frequently and deliberately erode the surface of the wheel to the level of
the deepest groove. If the wheel becomes out of true or uneven, an harmonic vibration may be set up that could damage the equipment or cause a dangerous breakage of the wheel. Finally, great care must be taken to spin silicon carbide wheels dry after
each use. If wheels are allowed to rest when wet, the water will settle in the bottom portion of the porous wheel. Upon startup, the unbalanced wheel can shatter with dangerous consequences.
Safety issues with diamond wheels are confined to protecting the eyes from flying particles and providing adequate ventilation of airborne particles, as should be done in any grinding or sanding operation.
In short, diamond is much better if you can afford it. I decided to start with silicon carbide grinding wheels and diamond sanding belts, and to upgrade to diamond wheels later, when I was able to afford the upgrade. Learning to grind on silicon
carbide, I figured, would make me more appreciative of diamond when I finally got it.
Wheel diameter?
Cabbing wheels and disks are available in a variety of sizes, with cabbing units available to use each size.
The most common sizes for the lapidary hobbyist are 4", 6", and 8" diameter. 8" is also popular among professional lapidaries. Contempo Lapidary and Diamond Pacific both make 8" professional cabbing units. Some professional units are available
with wheels of 10" diameter or more, but these machines and accessories are quite expensive and not widely available.
Size matters in cabbing, because the perimeter of a larger wheel moves faster than the perimeter of a smaller wheel moving at the same spin rate in rpms. Most commercial units I was considering used 6" wheels and disks, and experienced lapidaries
recommended 6" as being adequate, so I chose to use 6" wheels and disks in my own design.
Solid sanding wheels or drums?
For peripheral sanding wheels, one may choose solid resin-backed sanding wheels, or one may select expandable rubber drums onto which replaceable sanding belts may be slipped. Sanding wheels like the Nova wheels by Diamond Pacific are available in
1-1/2" width. Expandable drums and sanding belts are available in that width, but also in 2-1/2" width. I chose the expandable drums in the wider width, because the extra width might make it easier to get an even surface on large cabs. Initial outlay
for the rubber drum and a diamond sanding belt is somewhat higher than for a diamond sanding wheel, but may eventually end up being somewhat less expensive because replacing the belts is less expensive than replacing an entire wheel.
Water delivery system?
A cabbing unit must provide for the delivery of a drip or spray of water to the wheel being used. Commercial units employ a variety of irrigation systems. Some provide for a tank with a slow drip that is positioned over the proper wheel. Some use
an air pump to spritz water up on the bottom of the wheel from below. Some use a water pump to recirculate water and spray it on the wheels.
I figured that more water must be better, to keep the wheels more flushed. I used a fountain pump and positionable spray arms to direct water from a catch pan under my unit onto the wheels. My wheels ended up well flushed, but I also ended up
soaked whenever I used my cabbing unit. The fountain pump solution is overkill. In next month's article I will explain my original irrigation system, and in the final article in this series I will show how I adapted that system to suit the practical
demands of cabbing much better.
Direct or belt drive?
Some cabbing units mount wheels on long shafts that protrude from each side of a specially designed motor. The Diamond Pacific cabbing stations use this style. The benefit is a more efficient transmittal of energy to the wheels, because a belt
drive involves losses to friction. Slippage of the belt is another possible problem which must be addressed by maintaining proper tension on the belt at all times. Finally, a direct drive system avoids the size issue of having to mount a separate motor
behind or below the cabber.
The motor for a direct drive unit must be specially designed to keep out moisture and grit, and should also be explosion proof. I did not have access to a suitable motor for a direct drive system, so I chose a belt system instead. The advantage
here is if one motor burns out, I can easily swap it.
Shaft size and material
As far as shafts are concerned, bigger is better. 5/8", 3/4" and 1" are all common in combo cabbing units. 1/2" is also found, and is fine in slant cabbers and flat-disk machines. It is probably too thin for multi-wheel units. The torsional
stresses placed on a long shaft bearing massive inert wheels can warp a shaft that is too thin. This in turn could eventually lead to a potentially dangerous high-speed mechanical breakdown.
Most cabbing wheels and drums are built with a 1" bore, and bushings are provided to fill the space between that bore and a thinner shaft. The highest end units use the largest shafts. In my case, the price difference between buying 3/4" steel and
1" steel stock was not very significant, and I had some 1" pillow block bearings, so I chose 1" stainless steel for my shaft.
The high end units (Contempo and Diamond Pacific, for example) use stainless steel for the shafts. Many other units use regular steel, which is more likely to rust. Rust problems are minimized by cleaning and drying the unit thoroughly after each
use, and by keeping it well lubricated. I chose stainless steel because I know I tend to neglect cleaning from time to time, and I wanted maximum durability. Stainless costs significantly more than non-stainless steel, but you may be able to find
suitable stainless steel stock at a scrap yard.
Variable speed control?
One desirable feature in a cabber is variable speed control. Optimal performance at various stages calls for different speeds of operation. Some materials may also finish up better at a particular speed. Some units offer speed control and others
don't. A DC motor permits speed variation more easily than an AC motor, which operates at multiples of line frequency (60 hz). Older style basic units vary speed by changing the relative size of the sheaves (pulleys) on either the motor or the cabber
shaft. Having a ready supply of scrap AC motors, I decided to forego speed control for now, and add it later, mechanically, by adding sheaves of varying diameters.
Shaft mounting hardware: nuts, flanges and spacers
Wheels and other accessories are held in place on the shaft by compression. At one end is some sort of stopper, and the shaft is covered along its length by spacers, then wheels mounted between flanges, then more spacers, etc. At the end, a
compression nut is tightened on threads and the force is distributed along the mounted components, ensuring that nothing can shift or rotate when the shaft is turning at full speed. The threads are cut in such a way that the turning of the shaft tends to
tighten the nut -- otherwise it would spin off and fly off the unit at speed. Note that if the shaft turns toward you, or counterclockwise when viewed from the right end, then the right hand nut will need to screw onto normal right hand threads. The
left hand nut, however, will need left hand threads. To understand why, visualize the shaft turning counterclockwise as viewed from the right side. As viewed from the left side, the same shaft is turning clockwise. This direction of turn will cause the
left hand nut to spin off if the left hand of the shaft is threaded with normal right hand threads. When you make your shaft, you will need to have left hand threads turned on the left end of the shaft, and will need to obtain a left-hand nut for that
end.
NOTE: turning left hand threads is special work, and will cost somewhat more to machine than right hand threads (for which most shops have die on hand). This is one compelling reason to go with a slant cabber or single wheel design like the Graves Cab
Mate or Contempo Multi Flex. These units only use the right hand end of a shaft, with right hand nuts. I am planning a future machine using this design principle, which will be smaller and more economical to build than the design I am describing here.
However, the present unit (my Leviathan) does permit cabbing without interruption to change accessories, which I really like.
The lowly flange turned out to be the trickiest part of my cabber design. A flange is a metal plate, shaped somewhat like a dished washer. Grinding wheels, saw blades, and rubber drums are held in their proper 90 degree orientation to the shaft by
a flange on either side which supports the wheel uniformly at some distance from the shaft. The flange diameter should be no less than 1/3 the diameter of the accessory for proper support (more is generally better).
I thought I could pick up suitable flanges at any hardware store. This is not the case. Suitable flanges must be ordered from a lapidary supply house or equipment manufacturer, or must be custom fabricated. Many suppliers had no idea what I was
talking about when I asked for flanges, or refused to sell them separately. I found that Contempo Lapidary was my best source, selling me 2-1/2" stamped steel flanges for around $5 per pair. Another source was Kingsley North Lapidary, which was willing
to special order some heavy cast flanges from one of their vendors. Those flanges were higher quality, but much more expensive at $20 per pair. I went with those from Contempo Lapidary, and have been satisfied with their quality.
When evaluating flanges, you must be sure that they fit snugly around the shaft, and that the rims of the flanges meet perfectly all around the edges. If the flanges are warped, they will put dangerous stress upon your wheel.
Spacers are also necessary. These can be cut from smooth pipe, as long as it is very uniform so as not to set up vibration. The cuts should be perfectly perpendicular to the length. PVC pipe may not be strong enough to hold up to the necessary
compression, and I steered clear of it. I settled on nylon "collars", which are spacers with set-screws in them to permit them to be screwed in place. They are non-corrosible and plenty strong. The set screws allowed me to fix two collars in place 1
mm outside of the bearings on each side of the unit, so that when I tighten the compression nuts I am applying pressure to the innermost collars instead of to the bearings themselves.
Everything that you put on the shaft must fit the shaft perfectly. This includes spacers, flanges, and all your accessories. It there is any play, then the weight not be distributed perfectly around the shaft. At high speed, this can cause
harmonics to be set up which could bend the shaft or break the equipment, with potentially dangerous consequences. Remember the bridge in Washington that permitted harmonics to develop in high wind, and blew itself apart? Heed that warning and be a
perfectionist on this point.
Shielding
A final safety as well as comfort feature of any cabbing unit is the shielding. As noted in the section on diamond versus silicon carbide, the shielding should not only protect you from spraying grit and water and rock debris, but must also provide
a safety barrier in the event that a stone pops loose or a silicone carbide wheel flies apart.
Most cabbing units use bent sheet metal for shielding. I do not have a bending brake for forming sheet metal, and so I decided to use a ready made steel mailbox, rural size, for my shielding. I was able to cut out holes in front of the lower half
of the wheels with my tin snips, and smooth the edges with a grinding point on my dremel tool. This shielding is not optimal for a number of reasons I will detail in next month's column, but it was at least as sturdy as that of most commercial units I
examined.
LOOKING BACK and LOOKING AHEAD
Before closing I want to thank all of the readers of last month's column who wrote such kind notes. I look forward to hearing from more of you in the future. Charles Zweerink (czwink@inetnebr.com) had two helpful suggestions to improve the design
of the tumbler in last month's column. First he recommends plugging the tumbler into a ground fault interrupter outlet, which will shut off power to the unit in case of a ground fault (which would happen, for example, if electricity started to leak into
spilled water). I think that is an excellent precaution and very much recommend it. A GFI can be wired into the switch box, in fact. One can also purchase power strips with built in GFI, and plug the unit into one of them. Charles' other suggestion
was to mount the motor on a pivoting platform, and use springs to push it outward and apply tension to the belt. That will allow the motor to move forward and the belt to slip in case one of the shafts were to jam. Another excellent idea, which I am
considering using to upgrade the motor mounting for Leviathan. Thanks, Charles!
In next month's (February's) column here in the Low-Budget Lapidary I will explain how I constructed the initial design, which I nicknamed "Leviathan I" for its enormous size and the amount of water it tended to splash onto me. In the course of
using Leviathan I learned a few lessons about optimizing cabbing unit designs. I implemented some significant improvements, and will unveil "Leviathan II" in March.
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Copyright, 1997 by Catherine Harrison
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Cate Harrison designs, fabricates and sells original jewelry designs using gemstones and beads. She teaches classes in jewelry and bead techniques at The Bead Lady in Champaign, Illinois. Her popular bead-netted vase kits are among the work that she sells
through her website. "My business is definitely moving in the direction of more lapidary work, as my experience grows. Lapidary has opened up a fascinating new world for me."
Cate Harrison's website is at http://s.psych.uiuc.edu/~charriso/willowdale.html and she welcomes email comments and questions at charriso@s.psych.uiuc.edu
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