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