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59
TUMBLING INFORMATION
The tumbling of stones has been going on in Nature for
eons of time, as anyone who has picked up a smooth and
rounded stone from a beach can testify. This process in
Nature is the same that man uses today to tumble polish
gemstones: rubbing one stone against another in an
abrasive substance, and generally in water. Man carries
the process a step further—uses machines (tumblers) to
achieve a high polish on his gemstones.
Tumblers can come in several kinds and dozens of shapes
and sizes, as described on the following pages. All use the
basic process of grinding, sanding, and polishing stones
through movement in a series of abrasives from coarse
to fine.
The steps in tumbling vary from the use of an extremely
fine polishing material for only a few hours to put a final
polish on a valuable gemstone, to the general sequence
of coarse grit (60/90) silicon carbide through three, four
or more polishing abrasives in subsequently finer grit, to
the final polishing step. This can take from a few days to
four to six weeks.
Most stones with a hardness of 5 to 7
1
/
2
on the Moh scale
(see page 71) will tumble polish well. Softer and harder
stones may still polish, but may require more or special
steps and abrasives to achieve a satisfactory polish. Some
stones will never polish no matter what you do to them.
Tumble polishing stones is an easy and great way to start
kids (and adults) on a lifelong interest in the natural world
around them. Finding your own rocks, and turning them
into shining marvels of Nature is a rewarding experience.
TUMBLE POLISHING
STONES
TYPES OF TUMBLERS
Shown is the 25RT
twenty five pound
Rotary Tumbler.
(See page 60.)
Shown is the
Mini-Sonic MT-10
Vibratory Tumbler
(See page 62.)
ROTARY
TUMBLERS
There are two main types of tumblers—the rotary and the
vibratory. The first tumblers were of the rotary type, where
a barrel revolves as it rides on two parallel revolving shafts.
The vibratory type sits and shakes, causing the load to move
within the barrel but without the harsher action of the rotary.
Both types require a series of abrasives starting with coarse
and working up to a fine polish.
Rotary tumblers are the most familiar type, and range
in barrel capacities from around 4 lbs. to commercial
sizes that will process hundreds of pounds of material.
The smaller units (2–4 lbs. capacity) are popular for
youngsters and beginners, but the less expensive kinds
have more maintenance problems. A well built rotary
tumbler can last for years, however, even decades, if
given care.
Rotary (barrel) tumblers are generally easy to load, require
a minimum of attention, and produce satisfactory results on
most stones and metals. Their main tumbling action abrades
away any sharp edges and points, leaving finished stones
with rounded surfaces and contours. Rotary tumblers are
not suitable for material that is pre-formed and desired to
retain it’s shape.
Rotary tumblers generally take more time to finish a load of
stones, from four to six weeks or more, depending on material
and abrasives used. They also use more grit per load, but
generally need fewer steps in the tumbling process, and less
attention the rest of the time.
Vibratory tumblers have either mechanical or electronic
drives. Mechanical units use motors for power, while the Mini
Sonic tumblers use magnetic energy. They have no moving
parts such as shafts, belts or pulleys, and are exceptionally
long lived.
The action in vibratory tumblers is more gentle than
that found in rotary tumblers. The barrel in a vibratory
tumbler remains stationary even as it vibrates, producing
a continuous movement of material and grit within
the barrel.
Because of their unique, gentle polishing action. vibratory
tumblers do not wear away the shapes of stones, so that they
retain their original form. Hearts and squares will come out
as hearts and squares. This makes vibratory tumblers ideal
for polishing preforms, carvings, metal jewelry, castings, etc.
Vibratory tumblers are generally faster in polishing a given
load of material than a rotary tumbler, but actual time can
vary from one day for a final polish on a preform to several
weeks on hard-to-polish stones when starting from scratch.
SEE PAGE 109 FOR BOOKS ON TUMBLING.
VIBRATORY
TUMBLERS