Dear Beth, one problem with setting any stone whether cabochon or
faceted is providing clearance for the bottom of the stone and
having a properly cut "prong seat" or a properly designed bezel.
Depending on the appearance of the cab and the design and use of the
jewelry, I will generally make the bezel from sheet and then cut out
the back to accommodate the curve of the stone.
Since this might not work with some designs, the previously
mentioned "addition of a ring of metal" inside the bezel is a good
one. This ring provides the actual seat for the stone. Carefully use
a round or bud bur(or similar shape) to put a downward slope to the
metal ring, so it will fit the bottom of the cab. This is cutting
the seat to fit the stone. The ring is placed high enough to support
the stone and prevent the bottom from contacting the base plate if
not cut out leaving the back open. You can use an unsoldered ring of
metal sheet or better still solder a wire loop or sheet metal ring
inside the bezel. Either method will work and provide support for
the stone above the base.
I personally prefer supporting the stone with a curved bottom to
"cutting the stone" to have a flat base, unless the base is totally
wasted and too, too deep.
Thanks for hearing my thoughts on this.