For setting stones 2.5mm diameter into solid metal or a thick
bezel… a 1mm or 1.2mm drill bit…big enough to resist breaking and
small enough to correct it’s position with ball burrs.
Ball burrs 1.5mm, 2.0mm, 2.3mm. By boring out progressively the hole
can be positioned more accurately as it’s diameter increases. No need
to bore all the way through, just enough clearance for the pavilion.
When you get to the 2.3mm ball burr you are looking at the
circumference and it’s relation to the surrounding area. This is
where the precise spacing of the stones (if there are many) is
accomplished. Also the distance from any other feature can be
determined by what you see. Boring with the 2.3mm ball burr should be
deep enough to have a small portion of vertical sides. This allows
the hartz burr to do the least amount of metal removal.
Hartz burr 2.5mm. The hartz burr is fine toothed compared to a ball
burr. The hartz cannot gouge out metal like the ball can so expect
it to do no more than gently cut the seat for the stone and bore the
hole to the final diameter. It’s the last chance to make that small
adjustment in the hole position. This is where the seating depth is
determined according to the thickness of the girdle, and the seating
angle is made to relate with other stones or to allow for an
asymmetrical girdle and/or variations in table heights. Often I have
to go back to a ball burr to make more room for the hartz burr.
For setting into claws, a pair of flat needle nose pliers to adjust
the prongs, a 1.5mm hartz burr to cut the basic notches, and a 1mm
flat graver to trim the notches. There are many variables with a claw
setting. Best scenario is a minimal cut with a 2.5mm hartz burr, the
stone clicks in and you trim and form the tips. But an un-even
girdle will have you trimming individual prongs if you care.
I see many prongs set by cutting a notch, bending the top bit out,
snapping the stone in, straightening the prong to lock the stone
into the notch, snipping the prong level with the table, and rounding
off the tips. This is the cheap way. Even cheaper if the stone has no
seat apart from the notches. I find that stones need to be fully
seated on a circle of metal with claws holding the stone hard against
the seat. That’s my view for a setting that can withstand a big hit
on the table.
The tips of the prongs or claws should (in my view again) flow from
a strong outer part to a perfect union with the stone at the inner
part with no gaps or steps, so that the setting can be rubbed against
a towel and no threads will be snagged. How this is achieved is
another story and has little to do with burrs or bits.
CNC stones and CNC settings are sure to be a great marriage. I just
look at the old and the new with equal scepticism.