Guy,
I have long been amazed that the tools industry has not picked up on
the need for burs with graduated (.25mm increments would be nice)
girdle thicknesses. I almost never see - and do not buy - stones with
knife edge girdles so 99.999% of my settings require “seat sculpting”
of one degree or another with ever greater effort and time following
increasingly thick girdles.
I mentioned this need to Eddie Bell of Rio Grande at a trade show
many years ago and he found it an interesting idea but so far such
burs haven’t made it to the pages of anybody’s tool catalogs.
My own approach for most prong sets (regular or irregular girdle
thickness) is to use a 45/70/90 setting bur as appropriate and make a
first cut in each prong where I want the actual seat to be. I then
make a second cut above the first. The distance between the first and
second being the girdle thickness established by measuring the girdle
via a microscope and a GIA stone guage (.10mm increments). Finally,
using the edge of the bur I carve away the remaining metal between
the two cuts resulting in a straight wall that matches the girdle
height.
You can also make your first cut catching all prongs at once with a
standard setting bur (straight wall with pavillion) cutting deeply
enough that there is a substantial amount of the cut above the girdle
to be the crown contact surface. If you then nick the outside of the
prong right at the upper girdle edge height with a graver or saw
blade you can induce the prong to bend to make its bend at that point
and avoid using the edge of the stone as a fulcrum point. Go shallow
with the nick at first and increase it as necessary. Too deep right
off the bat results in a thinned out prong by the time you finish it
off.
I do all of my setting under the microscope now - normally at 5X but
sometimes 10X - because I can actually see what I’m doing. Certainly
not an age issue :).
As for setting stones with girdles of varying thickness you have to
take them on a stone by stone and prong by prong basis but the
technique is pretty much the same as my first method, you just have
to mark the stone somehow (Sharpies work great) so it is always
oriented in the same way during trial fittings.
I have seen some setters use ball burs instead of stone setting burs
for the thicker girdles counting on the maleability of the metal to
form around the stone as the prongs are set. Not fine setting,
perhaps, but workable in many situations.
Les Brown
L F Brown Goldwork, Inc.
17 2nd St. East, Ste. 101
Kalispell, MT 59901
Studio: 406-257-1129
Toll Free: 877-203-1482
Fax: 406-752-0694