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George Hello!
I'll see if I can explain my method for "flush" (also called,
rubbed in, and gypsy) mounting stones. You asked for a tool
description; here's the whole enchilada. Compare (no you don't
need to measure) the stone to a ball bur that is smaller than
the stone. If you use the comparison method, you'll find it very
fast and accurate for creating a seat from your memory of the
differences between your chosen bur and the stone. Personally, I
rarely need the dimension of a stone, prefering to memorize the
compared difference between a bur and a stone. Use a 3 inch
brass guage for this (smooth the guage so it glides easily
(opens and closes) with one hand). Choose a ball bur 10 to 20%
smaller than the stone. Bur down just over (barely) half way
with the ball bur. Let's assume you've a;ready drilled a hole
!/2 to 2/3's the size of the stone. Now with your "comparison"
guage choose a 45o hart bur that is slightly smaller than the
stone. A good reference would be 5 to 10% smaller than your
stone. In the case of a 4mm stone use a 3.7 mm bur to create a
preliminary seat. Imagine the stone set with table level ,or
permissibly, slightly above the surrounding metal. Memorize the
table to girdle dimension and use your hart bur to duplicate
this intended dimension for your seat depth. Start the bur in
side "A" at 75o to 80o degrees and cut gently while rocking the
bur to 90o and completing the seat. Be careful not to create to
deep a bearing. Here's where it gets tricky. The stone now, will
not go in the hole! Do not keep cutting deeper and deeper with
the hart bur! Choose a ball bur, a 3.7mm a good choice.
Carefully create a larger opening with the ball bur a little at
a time. Check your stone for fit often. Only try to fit the
stone the same way you cut the seat; side "A" first. If it still
does not go in use the hart bur to slightly increase the
diameter of the seat. You could take a 4mm hart bur and sharpen
with a thin separating disc, therefore decreasing the diameter
to say 3.8 to 3.9mm. Position the bur in your fingers to allow
cutting of the upper row of teeth. Follow the original angle and
tooth pattern as best you can. The bur will likely not last as
long as a machine cut pattern; but they don't make a 3.8 or
3.9mm hart bur! Start the bur in side "A" and rock to side "B"
gently and smoothly; easy on the pedal. While in the seat,ever
so carefully increase the seat size, being certain your cutting
level by rotating the piece. If the stone still will not go in,
your very close! Use the ball bur again. Oversize and check
stone for fit. Yes! The stone with a gentle thumbnail push,
snapped into place! (here we go George!) You now need a
"polished point" in a handle. Millgrain handles work well. Your
polished point is made from a worn out vanadium bur. The point
should be tapered to approximately one mm give or take. For
small stones (1mm to 2mm a smaller point is desired. For say a
6mm stone about a 1.25mm is prefered. Shape the tool to the
intended diameter by grinding, emery board etc. Final shaping is
accomplished by fitting in your handpiece and drawing it across
your emery paper, rubber wheel, etc. Final finish at your
polishing motor with tripoli (black works well on steel if you
have it) The point should be slightly domed, not rounded like
the tip of a pool cue. More like the chrome clicker on the top
of a pen. The edge should be more rolled than that however. Now
at near parellel to metal angle (even with table,plus 10
degrees) use even pressure, gently with the first go round. You
are burnishing the metal towards the stone, not down yet. Make
several passes until you can appreciably see you've effectively
moved the metal towards the stone. Now change your angle of
addressing the metal to approximately 65o to 70o degrees and
again burnish the metal. Start with light pressure,and evenly
burnish the metal back, this will smooth and tighten the stone.
You must be careful not to score the crown facets of your stone!
Even diamonds fall victim to this metthod of setting if due
caution is not constant! Invariably, you will swipe at a crown
facet occasionally, and scratch your polished point. Chuck it
up in your handpiece and renew it on a rubber wheel then hit it
on the tripoli buff. Now your ready to set another stone! There
are other methods to be sure. I used to use a wax pen and build
a little mountain range around each hole; what a mess! Hope
you'l ltry it, and it works for you!
Tim
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