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How to trim small cabochons?


#1

I bought some calibrated oval cabochons and some stamped gold
bezels, and I figured out how to set the stones in the bezels. But
maybe half of my stones are just a bit too big for the bezels. So I
have an old single-speed Dremel tool, and I’m trying to trim an
amethyst with a silicon carbide grinder, and it isn’t going well
because I haven’t figured out a good way to hold the 9x7 mm stone. I
stuck it ino a dopping stick sideways, that seems the most stable
configuration, and was able to grind it well enough, but then I’m
not sure how much to grind, and it’s tiresome having to take it out,
test it, then remelt the lacquer to put it back in and grind some
more. Is there an easier way? It seems too small to use a dopping
stick from the bottom, so that I could have access all around. I
tried putting it on upside down, but it just popped off.

Also, there’s some chipping on the downside of the stone. Does this
mean I’ll have to get a variable speed Dremel, or is there another
tool I should use? Is there some kind of magic tool for holding these
little buggers? I also have some 8x6 mm stones that need to be
trimmed, but just on the bottom to reduce the height.

DMGreer, LLC
www.luxefon.com


#2

Dale -

I guess that the real answer here is to work with a competent

lapidary to make certain that the stones you buy are suitable to
setting in pre-manufactured bezels. Off size stones are typical of
cheaply made (read tumbled) stones. These are roughed out by hand in
large, Third World factories, and then tumbled to a final
size/polish. Lacking any other evidence of this, these types of
stones can be immediately spotted by the dimple which normally
appears in the middle of the flat back due to tumbling. Working with
a lapidary resolves all the potential problems of trying to "adjust"
tumble finished stones on your own.

Jim Small
Small Wonders Lapidary


#3

Dale,

Try the following to reduce the size of your stones. First, I
assume you are dealing with faceted stones? Is that correct? If so,
take a wooden dowel (an aluminum rod can be used as well) that is
slightly smaller around than the girdle of the stone. With your
Dremel and a pointed reamer bur, cut a shallow cup into the top of
the dowel/rod. Now, heat some dopping wax or use shellac to build up
a thin layer on the inside of the cup. Wash the stone in alcohol to
remove any finger greese. Now, GENTLY heat the stone over an
alcohol lamp (don’t try this with heat sensitive stones such as opal)
until it is slightly hot to the touch - lay it aside and GENTLY heat
the wax/shellac until it becomes liquid. Now push the pavilion of
the stone into the cup until some wax/shellac comes out the side. Let
it cool completely. These are dopping instructions all lapidaries
learn in their first lesson.

Now you can use a fine diamond wheel to carefully shorten the girdle
of the stone to the diameter you need. You can either measure the
bezel and then the stone to determine if it has been shortened
enough, or you can simply push the table into the setting whilst
still on the dop and eyeball the fit.

To remove the stone, simply put the dop into your freezer for a few
minutes and it should drop right off the dop. Otherwise, gently heat
it until the wax/shellac softens and pull it off by a gentle twisting
action. Do NOT pull the stone straight out because, if there are any
weak areas in the surface of the stone, they will stay in the wax!

You can do the same process essentially with cabs!!

Cheers and hope that helps. Don at The Charles Belle Studio in SOFL
where simple elegance IS fine jewelry! @coralnut2


#4
   	I guess that the real answer here is to work with a competent
lapidary to make certain that the stones you buy are suitable to
setting in pre-manufactured bezels. 

Jim and All,

My experience is that stamped out bezels are too small for well
calibrated stones. If anyone has a source that makes bezels for a
stone that accurately measures 6mm-6.1mm (which would be reasonable
to me), let me know.

I use a diamond disc, 1 1/4 inch, on my flex shaft, diamond on one
side only. Sometimes you can bevel the bottom edge and get it to
wedge in. Otherwise, bevel the edge and then take a little off the
side. With the diamond disc I can hold it in my fingers.

Richard in Denver


#5

The cheapest way is to use 3M diamond files:
http://www.sculpt.com/catalog_98/Diamonds/files/3mfiles.htm

But they are a little costly here— I recently bought some more
from Wholesale tool for about 1/3 the price.
http://www.wttool.com/Merchant2/merchant.mvc

If you do a lot of this look at the Graves cabmate lapidary machine
or the all in one lapidary machine. jesse