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Building Jon Rolfe's Homebrew Faceting Machine
Part II.
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by Cate Harrison and Jon Rolfe
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In the last issue of the Eclectic Lapidary, Jon Rolfe and I provided some background on building a precision faceting machine, and described the design of the motor and electronic subsystem in detail. This month Jon and I will tell you how to construct
the faceting machine reference plane table and a wooden base to house and support the unit. At that point, you will be able to mount a purchased facet head, one of Wykoff's Calibrated Jamb Pegs, or any facet head of your own design. Then, in the third
installment of this series of articles, we will talk you through Jon's facet head design.
Subsystem 2: The Base and Table
The Table
The table of a faceting machine is far more important than one might think. It is the flat reference plane from which all other measurements are based, and upon which all other components are mounted in precise relation to one another. If there is any
sag in the reference plane, say, between the mast that supports the facet head and the spindle upon which the laps are mounted, then there is no way that you will be able to accurately facet gems, no matter how true the arbor or how precise the facet
head. There must be no flex or sag or unevenness here. It must be completely flat, so that the facet head assembly on one end of the table will be accurately referenced to the lap assembly mounted on the other. As Jon put it,
"The whole idea is accuracy. If the baseplate is curved, then the stone will have slightly different index angles at different distances from the center of the lap. It CAN be managed OK, but it takes some bother, and why work hard when building something
well will outperform the best commercial one? It is NOT just about saving $2-3,000..it's really about getting something better than can be bought at any price."
I first had to choose how large a table I needed, and then which material to construct it from.
The decision of table size was guided by the size of the laps I would use. Six inch laps are cheaper and would permit a smaller table. I wanted the option of cutting big stones at some point, so I chose 8" laps, which would still permit me to use 6" if
I chose. That means the table top had to accommodate a splash guard 9" in diameter, plus allow for the mast to move in and out sufficiently to provide for all the faceting angles I might need. Taking all those factors into account, I chose to use a 12"
deep by 18" wide table size. Jon's current machine is 18" x 24" and is mounted into a desk, but my machine needed to be somewhat transportable and Jon agreed that these dimensions would be adequate.
Now to choose the material for the table. My options were 1/2" thick dead flat aluminum tooling plate milled accurate to +/- 0.005 per inch, or 3/4" thick cast acrylic. Jon explained to me that the acrylic sheet is cast between two sheets of glass, and
is dead flat when purchased. As I would have had to pay someone to mill the aluminum, this was by far a less expensive option for me, and I went with the acrylic. I got a 24" x 12" piece from McMaster Carr for less than $30.
Because plexi will tend to sag over time, Jon strongly urged that it be stiffened underneath with aluminum channel. Says Jon,
"I used 4" X 1" channel, shaped like a "U". It's the stuff McMaster-Carr sells. This prevents the plastic from sagging.
Cutting the Table
Several holes must be cut in the plexi or aluminum table in order to mount the stiffeners to it as well as to accommodate the motor on one end and the mast on the other. I took my plexi to a local plastics shop for accurate cutting. First they cut it to
size (12"x18" from 12"x24"). Then they drilled a 2" core, centered equidistant from the left end and the top and bottom, through which the lap mounting flange on my motor spindle (see last month's installment in this series) could fit easily. The motor
would mount below the table with the flange and spindle rising up through this hole to the top side of the table. The plastics folks also measured my motor bolt circle and drilled four counter sunk bolt holes to mount the motor. Here is what Jon had to
say about holes for mounting the motor:
"You do not need to tap because the threads are in the motor. Just use clearance holes and countersink. The screws will go right through into the motor and should be flush countersunk to the top of the plexi."
The only other hole I had drilled was to mount the mast assembly. Jon's mast assembly (which will be detailed in next month's final installment) has a dead flat aluminum "foot" that rests upon the reference table. This foot has a long slot in it. A
bolt passing up through a single 3/8" hole in the table will rise through this slot. A large washer and knurled knob tightens down on this bolt, clamping the mast assembly foot firmly in any position on the table. Here is Jon's reply to my questions as
to where to place the mast mounting hole on my table:
"Mine is 10.5 inches from the centerline of the spindle/motor shaft. But my base is big..24"X18". No hurry on that. Wait till you get the head, and then you can lay it out and eyeball it. It is the only thing which is NOT critical! ... As long as it
is moved inward on any radial, it [placement of the hole] does not matter. I did it offset for comfort, allowing for the base size, the length of my arm, the height of the chair I use, etc. But you must realize I have put hundreds and hundreds of hours
in (Till this job!), so had time to "tune" it for me...."
"So any distance from 9-10" will be fine... and drill the hole on the same center as the spindle, or to put it another way, on the 90 degree radial. In addition to moving in and out, the base of the mast of course will swivel about the bolt hole, giving
very wide adjustment. This is needed because a riser to elevate the lap is used when faceting girdles."
I chose to position the mast mounting hole 4" in from the back and 4" in from the right side of the table. This works out to around 11.2" straight line distance from the center of the motor spindle to the center of the bolt hole, and provides me plenty
of landscape to maneuver the mast foot around on the table. That placement made sense considering my planned placement of the stiffeners underneath the table, which would interfere with the large, machined flat washer at the head of the mast mounting
bolt (again, more on this next month). Again, the plastics people drilled this hole for me.
I have not yet added the stiffeners under my plexi. I plan either to do so before the end of 1997, or to upgrade to an aluminum baseplate.
The Splash Guards
Jon and I discussed splash guards at some length, and I finally settled, with his urging, on the simplest possible splash guard design. I simply cut a 9" ring of plastic from the rim of a plastic bowl (located by wandering through the housewares section
of Walmart, as Jon suggested), and used silicone aquarium sealer to seal it to the table, centered around the arbor. I cut a similar, smaller ring for the inner splash guard, which protects the spindle and the motor bearings from any stray "rock juice",
and cemented it in the same way. I cut a 1/2" drain hole in the plexi just inside the outer splash guard, at the back of the machine, and used more silicone to seal a length of clear plastic tubing to the inside of the hole. The other end of the tubing
exits through the back of the wood base (through another hole there), and a simple plastic bowl is positioned under the end of the tubing to catch the water that drains off. This very simple system has proved more than adequa!
te. I am careful to remove my laps and clean the entire drainage area after each use. Evidently plexi will take up water if left in constant contact, specially in very warm conditions, and this could cause warping over time.
The Base
Many people cut a hole in a tabletop to hold their faceter, but I chose a self-contained base. Any material could be used, but I chose wood -- poplar to be exact. It is hard, inexpensive, and durable. When stained darkly it has an attractive grain (it
tends toward greenish if stained only lightly). Unlike metal, it is an insulator. Components can easily be screwed directly to it, and it can be shaped and assembled using hand tools.
My DC motor (see the previous installment) is 5" deep, so I made the base 7" deep to permit plenty of cooling airflow as well as working room. I had the poplar accurately cut and joined at the mill where I purchased it. I chose not to miter the edges,
but simply butted 2 18" lengths of poplar over 2 10-1/2" lengths and screwed the resulting box together (I used 1" wood, which is actually 3/4" thick). Figure 1 shows the box early in its construction.
My simple construction method worked, but isn't optimal. When I later shipped my complete machine to Jon for his inspection, the wood around the screws on one side split due to harsh handling by the USPS, and had to be repaired with wood epoxy. Not a
catastrophe, but Jon assured me that I would have saved a lot of trouble and had a more sturdy product has I used aluminum angles in each of the 4 corners, and screwed the wood panels to that.
In any event, after constructing the wooden base I sanded and stained the wood with a walnut colored stain. Later I sanded and sealed with several coats of water-based polyurethane. When the surface was dry, I was ready to mount my electronic
components, the "guts" of the system, described in last month's installment. I drilled a hole in the lower back of the box to accommodate the power cord, and cut holes in the front of the box to accept two toggle switches and the variac for the speed
control. Figure 2 shows the completed box, stained and sealed, with the mounting holes cut into it.
Finally, I cut a sheet of aluminum, mounted the switches and variac to it, and screwed the aluminum to the front of the wood base. Figure 3 shows the wood base with some of the electronics mounted inside and the aluminum plate ready to be mounted over
the holes in the front.
Final Assembly
With the wood base constructed and the plexi table drilled, I was ready to assemble the beast. My initial plan called for holes through the plexi to screw the table onto the wood base, but I opted once again for the simplest option. With Jon's approval,
I simply made a thick bead of silicone sealer around the top of the wood base, and laid the table on top of it. As Jon suggested, "The silicone will distribute stresses, and will dampen vibration." It certainly made up for any irregularity in the
height of the wood base. The silicone aquarium sealer makes no claim to bonding wood or plexi, much less to one another. However, three days after sealing the table to the base in this manner, I boxed the whole machine up and drove it 1200 miles to
Texas. Since then I have also shipped it to Jon's place (he added some more silicone to take the bead all the way out to the edge of the wood), and he has shipped it back, with no signs of any weakness in the seal.
Conclusion of Part II
In this installment we showed you how I assembled my own reference table and wooden base. The reference table's flatness is critical, but no other aspect of the table or base is rocket science. This is an area of the faceter design that is completely
modifiable to meet your needs. If you have tooling plate, by all means use it. If you want to mount the table into a desk instead of on a base, help yourself. Do take the time to think through your design. Although the table and base subsystem are the
least difficult design elements in building your own faceter, they may well prove the most important to your own comfort and convenience in the long run.
Next month, Jon and I will provide you with his mechanical drawings for and an explanation of the construction of the facet head and mast assembly. Don't miss it!
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Copyright, 1997 by Cate Harrison and Jon Rolfe
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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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