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The 75 Cent Salvation Army Hardwood Salad Bowl
Polishing Spool
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The first question that generally comes to mind when you look at a piece of equipment in the lapidary and mineral mags' ads is, "does it work?" Usually you figure, yes it does, or they wouldn't be advertising
it, and go on to the next question, actually questions, because they're all linked: how does it work, how well does it work, and can I use it for my own purposes? That's where you run into problems.
I don't suppose it's escaped anyone that there's not exactly a wealth of lapidary technical help in any of the mags, let alone practical comparisons between one style of machine or technique and another. There used to be, in the old (the old old) Lapidary
Journal. But that mostly went out even before the beads came in. So you fall back on word-of-mouth endorsements, which have their own drawbacks. And even these can be hard to come by if, like me, you live in an out of the way corner of the continent on
the fringe of the known universe where the distance from one lapidary to the next can be longer than a civil servant's lunch hour.
One technique that always intrigued me was polishing with diamond compound on hardwood polishing spools. They looked so different from the leather pad on the end of the arbour I was used to. But the constant shortage of reliable information coupled with
a frequent shortage of reliable income meant I wasn't going to run out and buy one just for the sake of experiment.
I knew that the maple spools pictured in the magazine ads had grooves turned in them to fit the curvatures of a stone. Similarly, the two metal diamond discs that came with the Graves Cab-Mate I recently
inherited were likewise dished, for the same purpose. Thus mentally prepared to do cab work on the inside of a hollowed out surface, it didn't take any rocket science to see cabbing possibilities in the hardwood bowls on the shelf of the local Salvation
Army store at 75 cents each.
They were about 6 inches in diameter, just the right size for the Cab Mate, turned on a lathe (which meant centering would be easy) from some species of hardwood which my untrained eye suspects might be birch. A raised flat ring had been turned on the
bottom, so they worldn't wobble on the table. All that was left to do was to make up a flange with a screw in it that would fit into the threaded hole in my arbour. And
here's the procedure in detail.
Illustrations #1 and #2 show two views of the bowl. I cut out a brass disc about 1/16" thick of a diameter to exactly fit the base of the bowl. The disc would be held on with wood screws going into the raised ring of wood at the bottom, so I drilled a
ring of eight holes evenly spaced around the flange disc, such that the screws would go into the centre of the raise.
The "shaft" of the bowl assembly is simply a brass machine screw (illustration # 3) which screws into the internal arbour thread on the Cab Mate . Since the pressure of polishing a cab against the inside of
the spinning bowl concentrates a fair amount of strain on that (rather slender, I think it's a number 12) machine screw, I wanted to make a joint that was both as firm as possible, and also would take some of the
strain off the screw. To that end I cut out a brass washer about 1" in diameter and drilled a hole in it to snugly fit the machine screw. I'd previously countersunk the inside of the centre hole in the big brass
disc, to give as much bearing surface as possible to the machine screw on that side. The top surface of the nut also would mate up flush against the end surface of the arbour when the finished spool was screwed in, again taking more of the strain off the
screw itself.
The machine screw went into the flange disc, the washer was slipped over it, and the whole was held together by turning the nut tight up against the washer. After a quick check that the screw was in fact
perpendicular to the flange plate, the assembly was thoroughly fluxed and all joints were silver soldered, nut to screw, screw to washer, washer to flange plate. Likewise the head of the screw was silver soldered into its countersunk hole from the other
side of the plate. With the flange plate screwed into the bowl base (use screws short enough that they don't come through into the inside of the bowl), the final assembly (illustration # 4), was ready for its first test spin.
I should add that basically the same can be done for externally threaded arbours. In this case, instead of a screw you'd silver solder (perhaps brazeing would be preferable, for greater strength) a nut of the appropriate diameter onto the centre of the
flange plate. Although it's more difficult to centre a nut, it can be done.
Needless to say the first run was a bit wobbly. But not too bad, probably not more than 1/16" off. Since the inside would be the working surface, I left the outside as it was, parked a heavy steel block in front of the spinning bowl to serve as a tool
rest, and with a curved chisel turned out the inside of the bowl until it ran nice and smooth.
The last step was to fill the bowl with hot wax (real hot!) and leave it in the oven at 300 degrees for an hour. The intent of that was waterproofing the wood. But it was probably overkill, since I almost never use water on it, and the diamond compound I
use is grease based anyway.
And that's all there is to it. I use two of these, one with diamond compound of circa 2,500 grit (I can't read what's on the tube, it's in Russian...and that's another story too!), and the other (also Russian) of about 15,000 grit. But that's really
guessing. The former leaves just a hint of satiny cloudiness, the second gives a real crisp high polish.
I've used both for about six months, neither has yet broken (if it does I'll make a new one), and both do the job wonderfully well. In fact, I use the Salvation Army bowl and diamond method on cabs now at least
as often as leather and cerium oxide. It seems to me it does a better job on labradorite than the latter, and I've even used it semi-successfully to polish jade, (which may be more the fault of the jade than the of the bowl), applying the usual high
pressure to generate heat. And still the bowl survived. Not a bad investment, at 75 cents, a bit of time, and a lot of fun.
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Copyright, 1997 by Hans Durstling
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Hans Durstling is a freelance writer, jewellery maker and stone cutter living in Moncton, New Brunswick, Canada, near the zeolite, agate and amethyst collecting areas on the Bay of Fundy. His stories, reviews and commentaries have appeared in Canadian
Geographic Magazine, The European, Toronto Globe & Mail, Canadian Mineralogist, Mineralienwelt, Rock & Gem and many others. He now works primarily in corporate & industrial writing explaining complex scientific and technical products and processes to
layman readers, and writing & narrating corporate & technical videos. A considerable portion of his time is taken up with the constant battle to keep minerals and gems ("the hobby that got out of control") from taking over entirely.
Hans can be reached at sinico@nbnet.nb.ca.
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