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The Return of
The Low Budget Lapidary
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To begin, a disclaimer is in order. This article describes an amateur design of potentially dangerous equipment. I do not recommend that anyone try to duplicate this machine, which, though it hasn't killed me yet, may do so in
the future. My hope is that reading about the challenges I faced in making this unit may give you a better understanding of your own equipment, or may provide you with ideas that you can use in your own projects. Just bear in mind that by trade I'm a
cognitive neuroscientist, not a machinist -- so please apply due skepticism to my approaches.
This article is the much delayed parts 2 and 3 of a series which started last January with a background and terminology section. My apologies to readers (and to our dear editor, Carol) who have written to ask when the rest would come.
When I decided to build instead of buy my first lapidary combination unit, I settled on a design in which multiple accessories could be mounted at the same time. I liked the design of the Diamond Pacific Genie, and used that as my starting point.
First stop was a metal junk yard. Over the course of several visits I scavenged a 1/2 hp 110 volt AC motor and pulley, a straight length of 1" diameter stainless steel for a shaft, and an arbor consisting of two 1" diameter pillow block bearings,
mounting brackets for the bearings, and a heavy steel base, pre-drilled with three pairs of mounting holes.
In order to provide maximum stability, I mounted the bearing brackets on the outer pairs of holes in the arbor base. I would use the central pair of holes to mount the arbor onto a baseboard and drain pan. My plain stainless shaft needed to be machined
into a shaft. A local machine shop put threads on both ends of the shaft, and also drilled and tapped the right-hand end to 1/4"-20 in order to accept screw-back accessories. Flats were also machined onto the shaft in order to accept the set screws for
the bearings and the inner collars (these are secured just outside the bearings, and bear the compression when accessories are tightened on). The right hand threading was all very straightforward, but the left hand threads on the left side were a special
order. Those threads must be left hand threads, or the spinning of the shaft would cause the nut on the left to spin loose and fly off (assuming standard direction of shaft rotation). My machinist didn't have a die for the left hand threads, so they had
to be turned on the lathe. To complete the arbor, I purchased left and right-hand nuts for the shaft, some nylon collars (to serve as spacers), and a 1" diameter arbor sheave (i.e. pulley) from a standard supply catalog (McMaster Carr). Flanges to
support my grinding and sanding accessories turned out to be specialty lapidary items. I ordered some very satisfactory ones from Contempo Lapidary Equipment in Sylmar, California.
To mount accessories, I assemble the desired sandwich of accessories (each within a pair of flanges) separated by nylon collars. At the threaded ends of the shaft, I tighten on the nuts, which applies pressure enough to hold the entire sandwich secure.
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Figure 1. With the shield removed, you can see the stainless steel shaft, pillow block bearings, angled steel mounting brackets, and steel arbor base (painted white). The steel shaft I had machined from 1" stainless scrap. The beaing blocks,
brackets, and arbor base were a lucky find, intact. The white nylon collars that I use as spacers are visible, as are the end nuts. The left hand threaded nut on the left was hard to find in stainless. I settled for regular steel, and painted it with
rustproofing paint (white). The motor, visible in back, is ancient but runs fine. You can also see in this photo the assembled base, including the galvanized steel bottom of the mailbox, to which I will later rivet the splash guard (top of the
mailbox). |
Figure 1 shows the arbor set up with only grinding wheels attached. Notice that accessories should be balanced in weight on each side of the shaft, in order to prevent a wobble from developing.
With the arbor assembled, I designed a support for the unit. What I arrived at was cheap and easy, but terribly heavy and bulky. I scavenged a heavy fiberglass pan and a piece of melamine covered particle board for my drain pan and base. For a shield
(which must be structurally strong to protect the operator in case of a high-speed wheel breakage) I bought a large steel mailbox (rural size). I disassembled the base of the mailbox from the curved top, and made a sandwich of the particle board, the
drain pan, a rubber gasket, the bottom of the mailbox, and the steel base of the arbor. Using the holes in the arbor as a guide, I drilled
through all these parts (Figure 2).
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Figure 2. Unassembled parts of the unit's base. From the left: galvanized steel mailbox bottom, melamine-covered particle board, red rubber gasketing, arbor base (soon to be painted white with rustproofing paint), and fiberglass pan. All parts are
drilled to accomodate the lag bolts which are visible sticking toward the camera out of the melamine particle board. They are already caulked in place. |
On the bottom of the particle board, I counter-sunk holes for the heads of two long bolts, and then used waterproof caulk to seal the heads in place. With the particle board face up, I threaded the fiberglass pan, the rubber gasket, and the mailbox base
onto the bolts. The arbor base is elevated by about an inch, so I cut some plastic tubing to fit over the bolts between the mailbox base and the arbor base. When I placed the arbor base in position on the bolts and tightened the nuts, these pieces of
tubing were compressed, and prevented water from leaking into the holes and out the bottom. Figure 1 shows the base unit with arbor assembled.
To form the shield, I simply removed the ends and cut holes in the front of the mailbox to allow hand access to the wheels, as well as a hole in back for the v-belt to run through from the motor pulley to the shaft pulley. Then I used pop rivets to
re-attach the mailbox to it's base. I simply lay the mailbox ends in place when I do not need access from the sides.
As for the motor, I mounted it on a separate piece of wood, and mounted that on the particle board behind the unit so that I can slide the motor forward to loosen the v-belt, and backward to tighten it.
My design prevents anything from flying forward to hit the operator. I neglected to enclose the motor, however, and painted a black stripe up my wall the first time I operated my unit wet. My temporary solution has been to put a cardboard box behind and
above the motor and belt to catch the fine spray that the v-belt throws. Note that my shield does prevent the motor from getting wet (very important!) but does not keep the belt dry. The motor is wired to an on-off switch with a ground-fault interrupter
to break the circuit in case of a short.
Figure 3 shows the completed unit. It's huge, and wet, so I've named it the Leviathan. The design would be much improved by replacing the mailbox shield (which is much too big) with a custom-made lexan shield. The lexan would be comparably strong, with
the added (and much needed) benefit of letting in a great deal of light. The base is also much large than it has to be (the base is sized according the fiberglass pan I was able to scavenge), making the overall weight of the unit excessive.
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Figure 3. The Leviathan, in its place of honor behind the toilet (we have a very small apartment). I used a grinding bit on my dremel tool to smooth the cut edges in the shield. The mailbox shield is too large (the smaller ones were too small), and
does not permit light to enter. I use a bright halogen light from over my head to light my work. Lexan shielding will be a big improvement. It would be best to have separate shielding for the left and for the right, isolating the bearings and the v-belt
from sideways splatter of water. The motor is mounted behind, out of sight, and you can see the cardboard box that catches the small (but staining) amount of spray the v-belt throws. I am not concerned with danger from the belt breaking, because the
back of the unit is not exposed to anyone. It would be better to enclose the motor and belt, however. |
I do very much like the fact that my unit permits multiple accessories to be mounted at once. I can mount two grinding wheels and four 2-1/2" rubber drums at one time, permitting me to go from rough grind to pre-polish without stopping to change wheels.
A spin-on polishing disk can be mounted on the right shaft end without any change to the setup. I also like the stainless 1" shaft, which is higher quality than most available commercial units provide.
A final word about water for the wheels. My original setup for water was a recirculating pump in the pan with an adjustable outlet that I could place over any wheel. This, of course, recirculated contamination onto my wheels. It also provides too much
water, which is difficult to control and ends up soaking me. My improved recirculating system places a 5-gallon bucket under a drain hole in the pan. The pump sits in the bucket, within a perforated can surrounded by particle filtering medium (from the
aquarium store). The holes in the can begin several inches above the bottom. A partition in the bucket prevents return water from being sucked directly into the can. It isn't lovely, but it seems to be preventing the contamination that was causing
scratches in my cabs before. My next step will be to have fixed drips above each wheel, which I can adjust as needed, perhaps using brass aquarium air valves (if they're air tight, they ought to be water tight, right?).
As you can see, my Leviathan is far from the perfect machine. If I had had a grand to drop on a commercial unit, you can bet I would have done it, in a heartbeat. Nonetheless, I have a very functional unit at a fraction of the cost. My expenses were
for machining the shaft (under $100) and purchasing the flanges and sheaves and a v-belt (under $50). I was given the silicon carbide grinding wheels by my pal and mentor Carol Bova, but will eventually replace them with diamond. I bought two rubber
drums to start ($44 each) and three 3M diamond belts ($35-65) from my pals at Kingsley North in Norway, Michigan. I estimate my total cost at around $400. However, I was very lucky in my scavenged finds.
Purchasing the components that I was able to find could easily push the cost of this unit to the level of excellent quality commercial units, which would be foolish, as the commercial units certainly avoid many of the problems that I'm still working
through with this unit.
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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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