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Setting - cone shaped hole


#1

I have been trying to learn how to set stones using various
techniques and most recently, bead setting and looking at prong
setting. In the process of getting together (making or buying) the
tools, I find a procedure that does not seem to make much sense to
me.

The stone sits in a cone cut by a 90 deg bur but as it would be a
strange coincidence for a pavilion to have exactly a 90 deg angle so
there can be no “proper” fit. If the angle is larger, the stone rests
on a circle around the pavilion and if it is smaller, it rests on the
culet.

The latter is obviously unacceptable and the former seems to have
worked for a few hundred years so my question is: why bother with a
cone shaped hole? Why not just use a straight drill of the size
required for the stone to rest a the required level?

js


#2

Jack S.

why use a cone shaped bur? you could try one of two methods, a round
or a bud shaped bur. these two methods are used by many of my peers.
my experience is to use the round bur. NO STONE SHOULD BE RESTING ON
ANY CULET. If you do, its curtains for that stone. Sometimes a
diamond might have a deeper pavillion or a wide girdle, hence the
decision to use one of these two shaped burs. If you look with a 10X+
loupe you will notice that the stone in question, is actually
"resting" or situated at the girdle, most of the gold is kept clear
of the pavillion. Most of the cone shaped burs bear little
resemblance to the angles of any diamond. What is your style of
"drill" is it a twist drill? of just another name for the above two
named burs? The “correct resting position” is to have the "table"
just at the surface of the surrounding metal. The culet must be fully
exposed, and not touching any metal !

I have another useful suggestion, how about clicking into my
web-site (and everyone reading this) and under INFORMATION and then
ARTICLES and/or TIPS then scroll down to retrieve "Claw Setting"
another useful essay (27 pages) very detailed “Tools for Stone
Setting”.

My site is www.gemzdiamondsetting.com this article will guide you
step-by-step through the world of 4 claw setting…“tools” took me
one month to write…

Jack, hope that this was a little help to you “Gerry, the
Cyber-Setter !” "www.gemzdiamondsetting.com


#3
why bother with a cone shaped hole? Why not just use a straight
drill of the size required for the stone to rest a the required
level? 

Somebody give that man a prize!!! :slight_smile:

Hi Jack,

You are absolutely correct. The hole should start out as a straight
hole (a “pilot” hole), maybe about 3/4 the diameter of the stone. The
hart burr is used to cut the seat for the girdle. Using a hart burr
to drill a cone shaped hole will result in rapid deterioration of
your burrs, as well as the problems you describe with the angle of
the seat.

If you have an opportunity, you should check out Blaine Lewis’ two
tape video on flush setting… or better yet, attend one of his one
week classes on stone setting. From your question, I’d say you have a
mind for this stuff!

All the best,

Dave Sebaste
Sebaste Studio
Charlotte, NC (USA)


#4
    You are absolutely correct. The hole should start out as a
straight hole (a "pilot" hole), maybe about 3/4 the diameter of the
stone. The hart burr is used to cut the seat for the girdle.... 

Roger but that was not exactly my question.

After doing as you suggest, you are left with a truncated cone with
a hole at the bottom. Using a 90 deg bur you get a 90 deg cone. A
typical faceted stone would have in included pavilion angle greater
the 90 so the stone would only rest on the top edge of the cone.

If this is the case, then a straight hole slighty smaller than the
girdle would produce the same support without the need for burs.

js


#5
 If this is the case, then a straight hole slighty smaller than
the girdle would produce the same support without the need for
burs. 

That is true, but also the metal under the stone re-directs the light
that passes through the stone- if the hole were only slightly smaller
than the stone, all that light would be lost.

Betsy


#6
If this is the case, then a straight hole slighty smaller than the
girdle would produce the same support without the need for burs. 

Not exactly. If the straight-sided hole were slightly smaller than
the girdle, the stone would be resting on a sharp edge of metal, high
on the pavilion, just below the girdle. Try to visualize the sharp 90
degree angle perpendicular to the angle of the pavilion. The sharp
edge of the metal on which the stone rests would put a lot of stress
on the girdle, possibly leading to a chipping or shearing off of a
section of girdle.

To set a stone in this manner would leave the girdle
ever-so-slightly above the surface of the metal. To set a
bead-n-bright or pave in this manner would require you to raise the
bead from the surface of the surrounding metal up and over the girdle
and onto the edge of the crown. This would be difficult to do and
provide a secure setting. With the girdle below the surface, you
raise the bead and force it down on the edge of the crown.

If you were able to successfully set the stone(s), the girdle being
above the surface of the metal would increase the probability of the
stone(s) being ripped out of the setting under normal use conditions
of bumping, rubbing, snagging, etc.

Although a seat cut by a hart burr might not exactly match the angle
of the pavilion, there is going to be more “cradling” support for the
stone. This also allows the girdle to rest slightly below the surface
of the metal, protecting the stone and providing a more secure
setting. Viewed from the side, I would only expect to see (ballpark)
about half to 2/3 the stone’s crown rising above the surface of the
metal. The stone is nestled down in its little hole, without the
vulnerable girdle and the beads being exposed to the harsh realities
of day-to-day wear and tear.

To flush set, as opposed to bead-n-bright or pave, the girdle must
be below the surface of the metal, as the metal from the surface of
forced down over the girdle. There is now way (at least that I can
imagine) you could leverage that much metal up and over the entire
girdle to set the stone.

I hope this makes sense! I don’t want to discourage you from
exploring new ideas or techniques. In this case, I think fairly
conventional wisdom will save you some frustration and damage/lost
stones.

All the best,

Dave Sebaste
Sebaste Studio
Charlotte, NC (USA)


#7
     If this is the case, then a straight hole slighty smaller

than the girdle would produce the same support without the need for
burs.

    That is true, but also the metal under the stone re-directs
the light that passes through the stone- if the hole were only
slightly smaller than the stone, all that light would be lost. 

I don’t understand the last part but a properly cut stone does not
allow any light to pass through.

js


#8
    That is true, but also the metal under the stone re-directs
the light that passes through the stone- if the hole were only
slightly smaller than the stone, all that light would be lost. 

Jack, to bead-set a gemstone, you obviously need to drill a hole,
the diameter of which is at least as large as the stone’s girdle, or
it wouldn’t be possible to raise a bead above the stone to hold it
in place. In order to bead-set a stone however, you need a
cone-shaped seat to drop it below the surface of the metal. Sure,
you could drill a straight hole, then set the stone with prongs if
you wanted. But just go ahead and try to keep the stone seated level
on that hole while bending those prongs! Then again, there are
cone-shaped setting tools similar to beading tools that may work.

You also mentioned in your next post that the bur leaves a
"truncated cone." That’s essentially true, but since this truncated
cone is so relatively small when compared to the hole itself, you
should really think of it as what setters call it - a seat. This
seat only needs to be as deep as necessary to allow the stone’s
girdle to sit flush or near-flush with the top of the hole. That’s
what allows you to raise the bead next to the girdle, which allows
the stone to be set.

The bur’s angle of 90 degrees (that’d be a hart bur, a setting bur
is normally 45 and there are plenty of others from which to choose)
as compared to a pavilion’s angle just doesn’t apply because it is
used mainly (but not solely) to cut seats for these applications.
Round burs work better for me with bead settings, as do setting
burs. Hart burs I prefer for channel setting.

And of course it would be unlikely to find a stone with a 90 degree
pavilion or crown angle. Well-cut gemstones are designed with
pavilion and crown angles that are compatible with that particular
stone’s critical angle. That is the angle at which light can leave a
gemstone after bouncing around and refracting inside of it.
Technically speaking, little or no light should be redirected back
through a faceted gemstone from the pavilion side. In actuality
though, most faceted cut fall short of the Excellent
category and their visual qualities do change when set with
different colored metals. Transparent to semi-translucent cabochons
are a different story. The point is, the purpose of drilling a hole
for a setting entirely through the metal is, IMHO, twofold; First,
to be able to poke the stone out before final setting, i.e. to make
adjustments, and second, to facilitate cleaning. The critical angle
of a gemstone changes when body oils and grease are present, and
they need to be cleaned from behind to restore their beauty. The
purpose of a seat (truncated cone) is to provide a secure rest for
the stone.

After all of this rambling, I would like to make a request of you,
Jack. If you do manage to set stones with a straight hole, please
take some photos and post them to the forum. There are some bur
manufacturers who might pay a fortune to keep that info under wraps.

James in SoFL who would like to buy the world a Coke, and keep it
company


#9
the metal under the stone re-directs the light that passes through
the stone- if the hole were only slightly smaller than the stone,
all that light would be lost. 

Hmmm… I couldn’t let this pass without comment. This could be true
with poorly cut stones, but not with well cut stones. Ideally, little
light passes through a faceted stone, but it is reflected (refracted)
back to the viewer, providing the sparkle, or brilliance of the
stone. Think of all the stones set in tube settings, with almost no
metal on the underside of the stone.

The pavilion angle of the stone should be calculated by the cutter,
based on the refractive index of the cutting material. This provides
the correct facet angles on the lower part of the stone (pavilion) to
bend the light over to the other side of the stone, where it hits the
pavilion again and is bent back out the crown of the stone to the
viewer’s eye.

There is a bit of room for error in the angles, but if they are way
off, or not considered at all, the result is a “window” in the stone
that allows the light to pass through the pavilion, out the bottom of
the stone. This is considered flawed cutting under most
circumstances.

The purpose of the cone shaped hole is to support the pavilion of
the stone at an angle that approximates the pavilion angle. Any light
reflecting properties of this procedure are incidental, especially if
the straight pilot hole is in normal proportion to the size of the
stone.

All the best,

Dave Sebaste
Sebaste Studio
Charlotte, NC (USA)


#10
  I don't understand the last part but a properly cut stone does
not allow any light to pass through. 

hmm- my understanding is that gems are cut at angles to maximize
reflection of light. The principle of optics demand that some light
pass through any transparent substance/air interface, even as it
requires some to be internally reflected. Only opaque substances do
not allow any light to pass through. (That is, in the visible range-
many things we call “opaque” make excellent lenses for infrared or
microwave radiation.)

Betsy- returning to school soon… sigh


#11
    Not exactly. If the straight-sided hole were slightly smaller
than the girdle, the stone would be resting on a sharp edge of
metal, high on the pavilion, just below the girdle. Try to
visualize the sharp 90 degree angle perpendicular to the angle of
the pavilion. 

But if the angle of a cone shaped hole (90deg) is smaller than the
pav angle, they cone may look cool but the stone still rests only the
the very edge, exactly like a straight hole of the same diameter.

    To set a stone in this manner would leave the girdle
ever-so-slightly above the surface of the metal...... 

This is a point I missed earlier but could also be resolved with a
follow up drill just slightly larger than the girder to the depth of
the girdle. It would require 3 drills and only arguably easier than
a bur but for a beginner, requires little skill.

    Although a seat cut by a hart burr might not exactly match the
angle of the pavilion, there is going to be more "cradling" support
for the stone.... 

This is where I have to disagree. The stone rests on a circle
unless the angle is exactly the same as the pavilion.

js


#12

One comment about this discussion–

I took Blaine Lewis’ stone-setting class. Flush setting is the only
style I learned there that I really use so far, and I’m no expert.
But Blaine (with his amazing magnification set-up) was able to show
us that, if you made the seat nice and narrow (you really only need
like 1mm), a diamond pressed into it will simply reshape it to the
angle needed, with tiny indentations for each facet junction. This
does not require applying extra pressure. Even with softer stones,
if the seat is only as big as needed to keep the stone from slipping
through, the pressure cannot be significantly away from the girdle.

And, of course, with a well-cut stone, all the light coming out the
top came in through the top, regardless of whether it is all open,
as in a tension setting, or all closed, as in flush or bezel.

I like flush setting so much that if I want a small stone set in a
"thick bezel", I don’t make a tube setting any more-- I solder a
tiny disc of thick gold where I want the stone, then flush set in
it.

–Noel


#13
hmm- my understanding is that gems are cut at angles to _maximize_
reflection of light. The principle of optics demand that some
light pass through any transparent substance/air interface, even as
it requires some to be internally reflected. 

This is true Betsy, but not in the way you imagine. As I mentioned
in the last post, faceted gemstones are cut with angles greater than
their material’s Critical Angle, not Refractive Index as has been
mentioned. What happens in a faceted gem is that when light enters
through the crown (nobody explains light entering through the
pavilion because most gems are mounted and worn crown-up), it bends
and slows down. How much it bends and slows is it’s Refractive Index
(RI). The light travels down to the inside of a (or some) pavilion
facet(s) and either strikes outside of the material’s Critical Angle
and reflects (and refracts again) off of it, or it strikes inside
the stone’s Critical Angle and exits. If the gem were cut with it’s
pavilion inside the Critical Angle, most of the light would exit
through the pavilion (Gemologists call this Unplanned Light Leakage)
and the stone would have no brilliance.

To understand critical angle, imagine looking at a horizontal facet
from the side. Let’s say a table facet. Looks like a simple straight
line, right? Now, imagine a cone protruding 90 degrees perpendicular
to the center of the facet, apex-up. When light enters inside that
cone from any direction (obviously from somewhere below), it is
within the Critical Angle and will leave the gem.

Each gem material has it’s own Critical Angle and good cutters try
to polish stones with the best proportions that also take into
account that gem’s CA. If cut properly, you can place any round
brilliant stone culet-down on printed paper and not be able to read
the print. Even table-down is difficult with high RI stones.

James in SoFl who wonders if my local ice cream parlor has Critical
Angle cones


#14

G’day.

A first class jeweller once demonstrated to me personally, exactly
how bead setting should be done, and why. The girdle of the stone
must rest on a seat a little (around 0.2 mm or a little less) below
the surface of the metal. A very sharp ‘vee’ graver is used to
produce towards the stone, a fairly deep groove in the metal
starting a few mm from the gemstone. As the graver cuts the metal it
will push up a curl of the metal it has gouged out, in front of it,
and stop a very short distance from the girdle of the stone. This
curl is later formed into a bead using a tool with a tiny
hemispherical hollow at the end - which looks nice - but this does
not lock the stone in position. The graver will push a bump in the
metal in front of it and it is that which moves over the edge of the
girdle and holds it firmly in place; NOT the bead. Look at it with a
powerful loupe and you will see what I mean quite clearly. The bead
can be knocked off accidentally, but the tiny bump will continue to
hold the stone.

So to sum up;

  1. The girdle must rest on a shoulder in the setting hole so that
    it’s edge is a little below the surface of the metal.

  2. The graver must cut deep enough so that it pushes a bump and a
    curl of metal before it.

  3. It must be the tiny bump protruding slightly above the girdle
    that holds the stone

  4. The curl of metal may be formed into a little bead, on the
    understanding that it is NOT the bead holding the stone firmly in
    place, though it may help.

Anyone disagree?
So~~~~~~~~~~~~
–Cheers for now,
JohnB of Mapua, Nelson NZ


#15
    hmm- my understanding is that gems are cut at angles to
_maximize_ reflection of light. The principle of optics demand that
some light pass through any transparent substance/air interface,
even as it requires some to be internally reflected. Only opaque
substances do not allow any light to pass through. 

Well, perhaps it is a matter of semantics and I don’t recall who the
original poster was. I understood her to mean that light from a
hole in the bottom could pass through the stone to a viewer looking
into the table. This would be a window defect.

Light must “pass through” the stone from the top so it can be
reflected back out the top by the pavilion. The difference is the
meaning of “through”. It must not mean through and out the bottom.

js


#16
       In order to bead-set a stone however, you need a
cone-shaped seat to drop it below the surface of the metal..... 

I suppose I should gracefully give this one up. I feel like I am
telling a Robin how to build a next but let me try one more time.

Draw a 90 deg angle on a piece of paper.

Next do the same for a 93 deg angle. This is the included angle for
a brilliant with a 43 deg culet angle.

Now cut this out of the paper and place it into the 90 you drew.
You will find that it will only contact the “seat” at two points. In
the case a cut stone, it will contact at 16 points. This is true of
any pair of angles that are not exactly the same as long as you allow
a hole for the culet to clear.

When I hear the word seat, I think of the way valves seat in an
engine head. They are lapped in to produce identical angles on each
part.

If all of the above simple geometry is true, then there is no
difference between a drilled straight hole and a “seat” formed by a
conical bur. In both cases the stone rests on a circle of points not
a form fitting seat.

I am sure there are good reasons to use a bur but a better seat is
not one of them.

As a point of interest, I received a bunch of burs today from Rio
and seem to have missed something about using them.

I didn’t have a collet for my hand piece Dremel so I but it in my
B&D cordless drill and it seemed to work pretty well. Made a nice
neat hole the size of the bur which happened to be the size of the
stone (8mm) I was playing with. Couldn’t do much else with the bulky
tool but this much worked.

My collets arrived in the mail a little later and I found the Dremel
totally useless for this tool. I have a speed control on it but it
is still too fast and just chatters and screams. The drill runs
about 200 RPM so I gather most commercial flex tools can be run very
slow for this operation. Is this correct? The ones I see in the
catalogs don’t say anything about speed other than variable.

js


#17

James,

That was the best description of Critical Angles that I've heard.

Thanks. I may finally be able to explain it to my customers now, in
layman’s terms. Can you explain, to a non-faceter, how Critical Angle
is determined? Is there a chart available for various materials? Can
this be measured in a cut gemstone?

Douglas Zaruba
35 N. Market St.
Frederick, MD 21701
301 695-1107
@Douglas_Zaruba


#18
 When I hear the word seat, I think of the way valves seat in an
engine head. They are lapped in to produce identical angles on
each part. 

Now it’s starting to make a little sense to you, Jack. Automotive
valves aren’t faceted, so they fit perfectly flush in their seats.
Your original question asked about bead setting faceted stones. I
tried to explain that the seat involved in flush- or bead-setting is
necessary to support the stone under the girdle with said girdle
slightly below the surface of the metal. That is the function you’ve
been missing here. This is necessary to allow the bead to be raised
and set over the girdle from the top to hold the stone in place. I
suppose if your hands are strong enough, the metal is thick enough
and you’re willing to gouge deeply enough, you could set a stone the
way you imagined, but I think once you’ve tried it, you’ll see what
I mean.

My collets arrived in the mail a little later and I found the
Dremel totally useless for this tool.  I have a speed control on it
but it is still too fast and just chatters and screams.  The drill
runs about 200 RPM so I gather most commercial flex tools can be
run very slow for this operation. Is this correct?  The ones I see
in the catalogs don't say anything about speed other than variable. 

Yes, that’s essentially correct. Also, the flex tool most jewelers
use is usually (but not solely) rated between 1/10 and 1/4 HP which
provides more torque (and thus, control) at lower RPMs. Most are
also used with a variable foot pedal. The problem with a hand-held
Dremel is that the lowest setting is still running. A Foredom (or
other brand) flex shaft is off when your foot is off, and turns at
speed as you step on the pedal. It allows a lot more control. There
are so many attachments and handpieces for these, it would make for
an entire discussion board.

To help with the screaming and chattering, a bit of lube on the bur
may or may not help. Spit will work, but beeswax is better. Dave
Sebaste mentioned a product called Bur-life. I got mine just last
week and screwed the holder onto the front of my bench. The
difference with sawing, filing, bur use, etc is really significant.

A good quality flex shaft is expensive, but worth every penny. Mine
is the $60 version that can be found just about anywhere, including
Harbor Freight. However, I’ve used Phingst, Foredom, et al and can
attest to their superiority, especially where it comes to the
handpiece. Mine has some wobble in it that doesn’t occur with the
$250 and up friends’ Foredoms I’ve used. If you’re serious about a
flex shaft, buy quality. You won’t use it only for setting, I
promise.

James in SoFl where a lot of the weeds have burrs


#19
    Each gem material has it's own Critical Angle and good cutters
try to polish stones with the best proportions that also take into
account that gem's CA. If cut properly, you can place any round
brilliant stone culet-down on printed paper and not be able to
read the print. Even table-down is difficult with high RI stones. 

If you have ever seen a tube set or flush set stone, while it is on
the finger it is not receiving any light from the back. That is the
simplest way to understand that if a stone is cut properly, it never
has, never is, and never will be refracting or reflecting light from
the back.

I explain to my customers it is the same as a mirror. Light behind
the mirror cannot be observed from the front.

Richard in Denver


#20
That was the best description of Critical Angles that I've heard.
Thanks. I may finally be able to explain it to my customers now,
in layman's terms. 

Doug, I don’t mean to rain on the parade, but I read the same
description, and even though I have a vague general understanding of
how it works, I was left as befogged as before. I appreciate the
effort, but… I totally didn’t get the cone business.

Noel