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Question on trimming down 4mm cabs

I use a lot of 4mm round cabs in my jewelry and set them in
preformed bezel cups. Some of the 4mm cabs I buy are just slightly
larger than 4mm on the bottom and cannot be used without grinding
them down. What is the best method for doing this? What equipment
do I need?

Currently, I hold these little stones in my fingers and grind the
bottom edge away with an appropriate griding wheel using my
flexshaft. This really hurts my fingers (even with aligator skin) to
try to hold something so tiny, plus I grind off finger nails, and
sometime the stone goes flying and it takes forever to find it.

If anyone has any recommendations for making this easier, I’d
appreciate it.

Thanks, Elizabeth

Elizabeth, Glue the bottom of those cabs to a 3 mm diameter brass or
aluminumm rod or wooden dowel with 2-part epoxy After it sets, it’s
easy to turn down t he diameter by hand ona slightly abrasive wheel I
recommend 600 grit, lig ht pressure, go slowly


Hi Elizabeth,

 I use a lot of 4mm round cabs in my jewelry and set them in
preformed bezel cups.  Some of the 4mm cabs I buy are just
slightly larger than 4mm on the bottom and cannot be used without
grinding them down.  

Unless the stones are expensive, why not by more than you need. Then
sort through them until you have a sufficent number of exactly 4mm

Sort the remainder into identical sizes & use them with the correct
size bezel cup.

If the correct size bezel cup isn’t commercially available, get the
closest smaller size & resize it. This can be done by making a punch
the correct size & shape. Lub the business end of the punch & drive
it into the smaller bezel cup.


Elizabeth, I would get some nails of the appropriate diameter to
super glue your stones on to. First find the right size nail.
Second grind the head of the nail flat and grind off the point of the
nail. A silicon grinding wheel in your flex shaft will do the
grinding. Super glue the stone to the nail. I would glue the top of
the stone to the nail so that I could fit the stone into the bezel.
After the grinding is complete put the stone and nail in acetone and
in a couple of hours the stone will be loose.

Gerry Galarneau

Hi Elizabeth, Use thick crazy glue and glue your stone to the head of
a finishing nail. That makes it easy to hold and if you center it
well, you can easily turn the cab against any number of abrasive
sources to reduce it’s diameter precisely. Use acetone to dismount
the stone. Good luck!

Best regards,

Hello Elizabeth, Is your problem one of diameter or of thickness? I
wasn’t clear.

The best way to deal with this is to avoid it. If you are picking
out the stones yourself, then bring a mm gauge with you and know the
maximum height you can buy and avoid those that are too thick or
wide. If you are buying through the mail or over the phone, let you
supplier know the trouble you are having and ask them to ship you
cabs with thickness or width of no more than ‘x’ millimeters so you
avoid the problem altogether in the future.

For those fat cabs you still have on hand, all you need to do is dop
them. Dopping is where you “glue” the stone to a stick with wax or
some other adhesive. Then you can easily hold tiny stones while you
grind away to your hearts desire.

You can dop to just about any small, strong, stick-like thing. I
regularly use skewers, pencils and golf tees, but notice the dop
stick I use are always made of wood. Golf tee’s are my favorite
because they are strong and the perfect length. I use the fat end for
bigger stones and the small end for small ones . Since you are using
a flex shaft to grind the stone, the length of the dop stick can be
as long as you want, but if you ever got into lapidary you would want
to keep them about 3" in case it gets away from you so it doesn’t get
jammed into the wheels of your lapidary machine.

Whether you need to skinny up the diameter or reduce the thickness,
you will need to dop first. If you need to skinny up the diameter,
then dop the back to the stick. If you need to reduce the thickness,
you need to dop to the front of the stone. To dop, first make sure
your stone is clean so the wax will stick to it. You need a bit of
dop wax (I like the green stuff), melt it in a little cat food can or
something small and metal like that. You can set the can on a
soldering tripod and heat the bottom till it the wax melts. It should
be melted to the point of queso dip…kind of thick but not runny. If
it’s too hot it will be runny and won’t hold. Dip the dop stick into
the wax and stir it around until it gather a glob. Let it cool a
teensy bit. Then form the wax into a mound kind of quickly (the wax
will be hot and will burn your fingers mildly if you hold in one spot
too long…this is how you will know it’s the right temp) and press
your stone onto the blob of wax and let this cool completely. Then
you grind away the unwanted parts. If you are grinding the bottom,
don’t hold too hard against the grinding wheel or it could come loose
and you’d be hunting again. To get it off the dop stick when you are
done, put it in the freezer till it gets cold and then just pop it
off. If it’s an opal, skip the freezer part and just pry it off.

You can also dop with epoxy and then soak it in acetone to remove,
but you have to be sure the stone is not going to be damaged in the

If you are reducing the thickness, the machine that would do this
the best is a flat lap. For such a small stone, you don’t need to
invest in such a machine. Just use an aggressive grit (100) wheel and
do what you are doing. Hope this helps!

  Some of the 4mm cabs I buy are just slightly larger than 4mm on
the bottom and cannot be used without grinding them down.  What is
the best method for doing this? 

Hi Elizabeth, Let me suggest a different strategy. I know the walls
of the commercial bezel cups are rather thin, but depending on the
variance, it might be easier and more effective to enlarge the cup,
than to reduce the diameter of the stone.

Another valuable tip from the Blaine Lewis experience. Take a
setting burr (which has straight vertical walls and a cone on the
bottom), and grind the cone off with a bench grinder. Be sure not to
get the burr too hot and remove its temper. Dip in water frequently
while grinding. This leaves you with a drum burr, with teeth only on
the outside diameter. This adapted burr is awesome for cutting
outward on the inside of a bezel without cutting downward.

I made a set of these burrs in different sizes and use them all the
time. Especially valuable for oval settings when the stone is too
large, and you obviously can’t use a round burr.

If you must grind the stone, the classic suggestion would be to
"dop" the top of the stone to a dop stick so you can handle it and
rotate is against your grinding tool. This could be anything as small
as a nail, toothpick, etc. The adhesive to use is the question. You
might be able to get away with hot glue. Epoxy would be better, but
is harder to remove (acetone), and might affect some stones.
Traditional dop wax would work, but probably not worth the trouble if
you’re not really planning to do lapidary work.

All the best,
Dave Sebaste
Sebaste Studio and
Carolina Artisans’ Gallery
Charlotte, NC (USA)

  If anyone has any recommendations for making this easier, I'd
appreciate it. 

Elizabeth, try this. Get some relatively large carpentry nails.
Common nails, not brads. The ones with wider flat heads. Get nails
with heads slightly smaller than your cab size. Use a sanding disk
on your flex shaft, or a sanding stick., or just a file, to flatten
the top of the nail if it’s not already flat (some have a seam or
ridge along the top.) Stick your cab flat side up into a bit of
wax, put a SMALL drop of super glue on the nail head, and stick it to
the back of the cab. If the nail head is flat, and the cab level, the
nail will easily just balance there while the glue sets. Once the
glue is hard, you’ve now got a nicely dopped cab. spinning the nail
shank in your fingers against whatever abrasive you use will be easy
to do, making it simple to get the thing round. Check the size with
calipers, not your bezel, since the nail is in the way of the bezel,
of course. Most cabs can be lightly trimmed just with a moores
disk, using adalox (aluminum oxide abrasive on stiff paper) disks.
Or you can use little diamond wheels, especially if you get then with
a fine grit. Use them with a bit of water to keep things cool. If
your cab doesn’t like heat and you want to use sanding disks, use wet
or dry disks, but i don’t much like them as much (at least, the
moores versions), as they’re thin and floppy. But you can use them
wet, and it WILL work. once your stone is the right size, hold the
point end of the nail in a pliers or something, hit the shank of the
nail with a small hot torch flame, far enough back from the head of
the nail so the stone is nowhere near the flame. The nail will
quickly heat up enough to cause the glue to fail, releasing your
stone before it gets more than a very warm to the touch. If your
stone cannot take even this heat, then just soak in acetone for a
while. You can also do the same thing with lapidary dop wax, but
it’s messier and melts at a lower temp, so any warming of that small
stone will cause it to shift on the nail head. Or you can use fast
set epoxy. It too, will release when you heat the nail, at a
somewhat lower temp, sometimes. And I’ve also used double sided
tape, which then just lets you peel the stone off. It has to be a
good tape, though, like carpet tape, with a good adhesive. You have
to work a little more gingerly with small stones, as they can shift a
little more easily on the tape, if the stone warms up. but for what
your’e doing, it should be fine.

Hope that helps.
Peter Rowe

Grinding a small cab to fit a stamped bezel cup, A piece of brass
rod smaller than the diameter of the cab and super glue to hold it
on the “dop”. Heat the rod slightly when done, cab should pop off
with slight pressure. Some materials you have to be careful, they
will take more heat than they will pressure, material can be pulled
out the the surface with lapis. I use a diamond disk in my flex
shaft. The side of a cut off disk will work on most stone. Cut the
bottom at a slight angle so you taper from where it is the right
diameter making the bottom slightly smaller than the middle. Dop the
top, cut and fit.

I have a letter to the editor published in JCK in the August issue

about SI3 diamonds. Bottom line, GIA has a grading system that does
not include SI3, SI3 was created by the market to sell lower quality
stones at a better price by deception. If EGL certs a stone SI3, how
would GIA grade it. Those of you who sell diamonds, what do you
think? And does a stone with eye visible inclusion, apparent to your
customer, with no magnification pass as an SI?

Life is Good,
Richard in Denver

may I suggest stretching the bezel cups larger ? You might try a
spherical dapping tool, you may need to grind the end flat so that it
will fit into the recess, a worthwhile exercise to create a specific
tool as you use this size frequently…

Mark Clodius