Hello, I asked a question several weeks ago about whether anyone had
used or knows anything about the Graves spool polishing unit. It is
used to polish cabs with diamond pastes and doesn’t heat the stone.
I never saw it posted and now that I see the rules for posting I
wonder does this fall into the categories allowed? I’ve seen so many
asking questions about stones both polishing and drilling. Thank You,
Christine
Hello Christine I used a similar polishing unit. The one I used was
wooden. The problem was the diameter of the wheel. It didn’t give
enough surface speed. I went back to a different system of disk
polishing. With the disk I could control the speed by working the cab
further out from the center (faster), or near the center for slower.
The kit I use is from Crystallite. There are other companies that
make similar products. Make sure if you go the disk route, that you
can change disks easily. Steve Ramsdell
I’ve used spool machines to polish with and still do with some hard
to polish stones. They work just fine, they are somewhat slower than
most other cab machines but on the other hand they are very quiet. I
would suggest running it with diamond borts or pastes on all but one
wheel and I would save that one for cerium because quartz can be tuff
to polish on diamond. You can use most any grit size in diamond
probably ending with 50,000. The other nice thing about them is that
they are small. Hope that helped…
cutter12
Christine:
I have a unit that is very similar to the Graves you mention.
Pressed wood spools used with diamond pastes in graded sizes to 50K.
Having cabbed with both this unit and various horizontal shaft units,
I can say a bit about it. While the heat wasn’t excessive for me,
actually I think it generates more heat than a water cooled unit used
gently. Remember, there is only the diamond’s paste carrier for
lubrication. The unit is somewhat cool because the stone contacts
the wheel in only one spot at a time. If you press hard and keep the
stone on the wheel constantly, you can generate some heat, but I know
people have successfully polished opal and other sensitive gems on
this type of machine by paying attention and cooling the stone as
needed. Press it to your lip from time to time and use a water glass
to cool the stone, but don’t shock it. If it does get hot, blow on
it till it’s cool enough to put in the water or to start again.
Heat with a horizontal shaft unit gets excessive when you push hard
on a rubber backed wheel and get much of the stone in contact with
the wheel at one time and keep it there. Copious water will help
some, but not obviate the need for a somewhat light touch and
checking as above.
The advantage of the Graves type unit is that it is small,
inexpensive (at least mine was years ago) and could be used on the
kitchen table. It can also be used on star sapphire and other hard
stones with good results. The problem with these units, for me, is
that they contact the stone only at one point, and so require endless
quick movement to keep from getting flat spots and to produce a
decent smooth rounded surface. The same result is forthcoming with
less time and less effort with a rubber backed wheel which conforms
to the shape of the cab to some extent and tends to produce a convex
surface. One needs to sweep the stone across, but one needn’t be
scrupulous in hitting every spot evenly as on the wood spool unit.
Also, the vertical shaft units include a grinder to rough out the
stone, and the wood spool units begin with about 325 grit, I think,
so roughing out the stone first on a rough grinding wheel or lap is
necessary. The early steps on the wood spool unit take forever as
one has to hit each flat spot numerous times from various angles to
produce a curve.
If money is an issue and that is why the wood spool unit is chosen,
one might want to look at a vertical shaft unit, some home made
wooden laps and silicon carbide disks with stick on cement, and a
felt and a leather polishing disk. Sinkankas’ book, Gem Cutting,
covers how to use these units for cabbing. A little less convenient
than the bigger horizontal shaft units, but cheaper and much more
portable and smaller. It is easy enough to build a vertical shaft
lap with a wooden box to fit, a washing machine motor and a couple of
pulleys and a vertical arbor.
HTH,
Roy
The advantage of the wooden spool is if you are cutting material that
has a tendancy to undercut or you are cutting very hard matr’l i.e.
corrundum. Otherwise it’s the most difficult and tedious process.
Hi Christine,
Rather than buying a hardwood spool polishing unit, why not make one?
It’s dead simple. I use flat discs sawn from flea market hardwood
cheese boards and hardwood salad bowls from the Salvation Army (guess
that would be “Goodwill” in the U.S.?).
Anyway if you want to see how to do it, I believe that my old story
“The 75-cent Salvation Army Hardwood Salad Bowl Polishing Spool” is
still online in the archives of the “Eclectic Lapidary” at
http://www.bovagems.com/eclectic.
My experience in using hardwood as a carrier for diamond
sanding/polishing is that it does generate heat, particularly when
polishing/sanding flats. It’s less apparent in a rounded stone. Also
diamond on wood tends to quickly wear channels into a stone,
particularly if it is a soft stone or one which has variations in
hardness. So you need to keep the stone moving, moving, moving, all
the time.
Diamond compound is typically grease-based. You don’t use water
cooling. In time, stone dust lessens the lubricating effect of the
grease. Dab on olive oil with your finger to restore it. Be aware that
oil and grease will mask imperfections. You can’t just give the stone
a wipe over your forearm to dry it the way you can with water, you
need a clean rag dampened with lighter fluid or something similar.
If you’re using diamond only for final polish, why not try 14,000
(and up) diamond in grease on a hard felt wheel. I find that gives me
an absolutely brilliant polish, at least one agates, which is what I
do most often. But watch the heat!
Cheers,
Hans Durstling
Moncton, Canada
Hi again, Christine,
For contouring and polishing, you can also use those pairs of
machined pine and/or oak disks made to hold up the ends of closet
rods, which are available at your local hardware store. For me, the
oak ones’ve served best for the initial, coarse-through-medium
sanding stages (since they’re more resistant to wear), while the
softer pine/spruce/cedar ones do better as polishers. Best of all,
they’re already pre-turned to concavity, so you don’t have to worry
about curvature differences, from wheel to wheel. (Just be sure not
to use the half of each pair that’s slotted to accept the
clothes-hanging rod: the vibrations caused by it, against your stone,
could easily damage both workpiece and artisan!
Best Regards,
Doug Turet
Hi Christine,
I agree with Hans on the vast majority of what he’s offered, except
the last part, about using diamond on felt. In my experience, while
felt makes a good buff for most Agates, Corundums and Nephrite Jade,
is a fine carrier for water-based oxide compounds (such as Cerium,
Aluminum, Tin or Chrome) and is as reliable as can be on metals, it
tends to heat up far too quickly for my tastes on most other
materials, often with disastrous results. Instead, I use a "padded"
wheel, made by sandwiching either four layers of burlap, or two of
that foam rubber-coated nylon netting that’s so popular, nowadays,
under a sheet of either canvas or denim. Try this with either 14,- or
50,000 mesh diamond compound at low speeds (<1,000 rpm) and don’t be
afraid of the “slap-slap-slap” sounds made by the buff; like your
Dad’s old shoe-shine kit, it gets the job done, and nicely so!
Glad to help,
Doug Turet