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INDEX
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The Low Budget Lapidary
and the Guppy
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If you read my last column about the Leviathan (my huge, wet, indestructible and utterly non-portable all-in-one cabbing workhorse), you may have detected some dissatisfaction on my part with the result. The cabs from that machine are lovely, and it is
quite convenient not to change belts, but in our small, crowded duplex I clearly needed more portable equipment. From my experience and frustration with the Leviathan was born my next cabbing unit: the Guppy.
Before I describe this cabbing unit construction project, let me make a few standard disclaimers. I'm not an engineer, I'm a cognitive neuropsychologist. I'm describing the construction of equipment that can electrocute you, blind you, mangle you, or
worse. So please take my experience for what it's worth, and only try building your own equipment if you know what you're doing. (What is it that the psychic hotlines say in fine print? "For entertainment purposes only...")
In order to keep a small footprint for this machine, I decided to have only one accessory mounted at a time. The motor would be mounted behind the arbor. The shield should be clear, to prevent the shadows that the Leviathan's mailbox splash guard cast
on my work. Easy cleanup was important. Simplicity was important. Easy machinability of materials was important, so I could do most of the work myself with my common hand tools. Yet the splash guard still had to be sturdy, for safety.
Polycarbonate plastic (lexan) was my secret weapon for this project. It is crystal clear yet extremely tough and strong, and it can be drilled and routed like wood and yet bent like metal. It's truly a miracle material. Note that this is not acrylic
(plexiglass), which has certain benefits, too, but is not satisfactory for a shield because it is more brittle and not nearly as strong as polycarbonate.
For a shaft I used an 8" section of stainless steel rod from the scrap yard, and two sealed ball bearings. I cut a stack of squares from 3/8" lexan sheet, just large enough for the ball bearing blocks to mount on top of them. I drilled holes through the
entire stack (4" high), so that the bearing blocks could be mounted with lag bolts through the lexan stack and to a base board sized 12"x24" and made of melamine-covered particleboard.
My friendly local machinist made an excellent custom flange for the inside of my arbor. The flange extends all along the shaft to the rightmost bearing, for complete stability, and is machined flat and 2" in diameter at the right-hand edge, providing
excellent support for whatever accessories mount against it. There is an additional 2" machined flat flange which can be used on the right of the accessory or as a spacer on the left, depending on the thickness of the accessory used. I have two pressed
sheetmetal flanges which serve as additional spacers or as the right hand support flange when needed -- they are not as accurate, but when the support on the left is so true they do not play as critical role, and are only needed to hold the accessory
against the true flange. The machinist also drilled and tapped the end of the shaft to accept 1/4-20 spin mounted disks and pads.
For my splash-guard and shield, I had a sheetmetal shop bend some 1/8" Lexan in a metal bending brake. They bent it into a "C" shape with 1" lips extending from each tip of the C forming a box that is open on the right face. Then I cut 3/8" lexan for
the back and front of the shield. The piece in the back completely closes the back. The piece in front is only 2" high, providing a hand rest and allowing front access to the cabbing accessories. I drilled through the thin "C" shaped piece into the
edges of the 3/8 thick end pieces. Then I used a hand tap to tap the holes to 10-24 size, and used machine screws to machine screws to bolt the thinner "C" shaped box to the thicker structural ends. Then I drilled and tapped through the inside wall of
the "C" shape into the stack of Lexan supporting the bearings, and screwed the shield directly to the bearing support (after cutting a hole for the shaft to stick through). Finally I sealed all the edges of the shield with clear silicone aquarium
sealer.
I mounted a 1/3 HP AC motor by screwing its metal support into a separate piece of 3/8" thick lexan cut 11"x8". I put a 2-3-4" three-speed pulley on the arbor shaft and a 2" single speed pulley on the motor shaft. I positioned an appropriately sized
V-belt over the pulleys to communicate motor speed to the shaft (i.e. using the middle setting on the 3-speed pulley, which matches the motor pulley), and moved the motor back until the belt was tight. Then I drilled through the lexan motor base into the
cabbing unit's base with 2 holes on the far side of the motor. Now by dropping two bolts into those holes I can hold the motor in place, and by removing those bolts I free the motor in order to change the belt setting. I can adjust the motor distance
to accommodate different arbor speed settings by drilling additional holes in the base.
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| Figure 1. The Guppy Cabber, front view, motor not mounted. Note the lovely machined flanges on the shaft. In the base of the drip pan/splash guard are a pressed metal flange and the tightening nut.
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The photo shows what the unit looked like at this point. The lexan shield is nice and clear, which makes it easy for light to reach my work. I also think it makes it easy to demonstrate to beginners how the machine works. The kids I have demonstrated
this unit to have dubbed it "The Visible Machine" because you can see everything going on in it.
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| Figure 2. The Guppy Cabber and the separately mounted motor, with one boy added for scale. This cabber makes a great demo machine for kids, because they can see everything. NOTE! I have added a lexan guard over the belt and over the
motor! These are important safety features, not shown in these pictures.
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For safety, I used additional 1/8" lexan to build a housing over the motor (must keep water out of there!) and also over the front and top of the belt end of the shaft, so the belt won't slap me if it breaks during operation. I installed a plastic jug
with an aquarium air valve and some clear plastic tubing to supply a water drip to the cabbing accessories -- much less water than the Leviathan has, so less mess. I have to refill the jug, but it doesn't cause much inconvenience. These additions are
not shown in the illustration but are essential to the safety of the unit.
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| Figure 3. The Guppy Cabber with the motor base installed. Belt is removed for clarity. Note the bolt to the back left of the motor, which holds the motor baseplate to the unit base. As the previous picture caption indicates, I have
added a lexan guard over the belt and belt pulleys to the left, and over the entire motor (the motor shield is bent in a U-shape and screwed to the lexan motor base. This is important to keep water out of the motor, fingers out of the belt, and to
protect the eyes and face in case a belt breaks. Also not shown, a water bottle mounted on a dowel rod in front of the lexan arbor supports, with aquarium airline tubing (clear) carrying water to a brass drip valve fitting mounted through the top of the
shield.
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This design has been a tremendous benefit to me. The motor mount is easy to remove, leaving two pieces (motor and cabber) that are small enough and light enough to transport easily. The unit accommodates a 2-1/2" sanding drum, 1" grinding wheels,
grinding and polishing disks, and a trim saw blade. I plan to construct a saw blade table for the unit sometime in the near future. Anyone who can think of a simple and compatible design for that, please mail me!
Happy cabbing.
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Copyright, 1997 by Cate 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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