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Hand cabbing process


#1

All,

I’m practicing making cabs using agate on a Inland Lapidary Swaptop
series, and I have a question about the hand cabbing process on a
stone mounted on a dowel with dop wax.

I usually start using my 175 grit wheel. Typically after grinding
the edge, I start the bevel at 45 degrees and grind the stone while
twirling, gradually increasing the angle toward the center of the
stone until only a third of the top of the stone remains.

Then, after cleaning my equipment and my stone thoroughly, I’ll
switch to 325 grit. I’ll do a fast twirl from the edge to the nearly
the top of the stone. I’ll then start rocking the stone from edge to
center to edge, twirling as I go, to round the top.

When I look at what I just did under 10X magnification, however, I
see a bunch of lines, so I’ll do another twirl from edge to top. This
breaks up the lines into what appear facets roughly evenly coating
the stone like a compound eye from a bee or fly.

I repeat this at my next disk, which is 600 grit, and the result
from this is that the stone is now covered by a whole bunch more
smaller pits.

The book (P. Downing) seems to say that I have to be able to
completely get rid of all scratches, pits, and lines for each grit as
seen under 10X magnification, before I dare go to the next grit.

But I don’t see how I am able to do that, because when I try to work
on the pits, they just get bigger and cover the stone far more
assymetrically.

Just what am I suppose to be doing?

Thanks in advance,
Andrew Jonathan Fine


#2

Hand sanding. In my 35 years of silversmithing and lapidary
experience, there is no way on earth to not ‘facet’ a cab on a wheel.
Sorry if that wasn’t much help.

Michael
www.radharcknives.com


#3

Andrew, First let me say I do not particularly like cabbing on a flat
lap. Having said that, I used a homemade flat lap for many years and
produced beautiful cabs using it. But, I would much rather use a
vertical wheel. Its what one gets used to I guess.

Now then, from what you describe in the first two operations, things
seem to be going just fine. The 175 grit wheel is a bit fine to grind
agate but using a firm but easy hand (not too much heavy pressure)
the job can be done. I normally do my course agate grinding with 80
or 100 grit. Speed at this point is important as well as pressure.
You should use the highest speed you have. I don’t know what the
Swaptop’s top speed is but such grinding should be done at around
2000 RPM if possible. At this point there is no sense looking at the
stone under 10x. All you will see is a bullseye effect with flat
circles separated by ridges. All you want at this point is a well
shaped stone with none of the ‘whiskers’ (short white lines) caused
by the abrading action of the first grinding wheel. The geometry
(shape around the girdle or widest part of the stone) which is done
first should be perfect and the dome (done second) should start from
just above the girdle up over the very top (crown) so that when
viewed from each end and side in silhouette all angles are even and
form a gentle curve.

This is where things should change. You say you next use a 600
wheel…is it a hard plate If so that is defeating your efforts to
smooth the surface. The next two or three stages should be done on
plates that have sponge rubber or cork backing and topped by silicon
carbide paper or Crystal Pads (or some such thing) with diamond paste
on them. A 600 grit wheel will smooth any unevenness created by the
325 though agate will take some time. That should then be followed by
a 1200 plate and some people use a 14,000 plate for final polish on
agate. After each stage be sure to loupe the surface but don’t be
surprised if you continue to see some fine scratches up through 1200.
As long as there are no ridges, flat spots, pits (caused by soft
spots in the stone usually) or ‘whiskers’ you can proceed to polish
on the 14,000. Now, having said that, I almost always do a final
polish on a soft felt or soft leather wheel (again backed with rubber
or cork) with Cerium Oxide (best for any silicate family stone which
includes agate). The speed when polishing should be dialed down to
around 400 rpms or so and use considerable pressure. The wheel should
be kept damp (never wet as the stone will merely slip over the
surface but never dry either) and you will feel the stone dragging.

I’m not sure what you mean by ‘pits’ unless the agate you are
cutting has natural pits in it. If that is the case they will never
go away. But the cutting as I described above should not result in
pits. I hope this helps you a bit. Cheers from Don in SOFL


#4

Hi Andrew,

You don’t refer to what type of diamond discs you’re using, but I
use a series of the resin-bonded diamond discs that are attached to a
base plate with pressure sensitive adhesive. I also use a sponge in
between it and the base plate. I find that this smooths out a lot of
the “facets” you’re talking about.

The hard diamond discs I find are too aggressive and I only use one
for my initial grinding. You have a lot more effect on the stone with
these discs because they are so much more forgiving than the hard
diamond discs. It has taken me a long time to find the series of
discs that works for me.

Dana Evans


#5

i also use an inland flat lap. sometimes i will get a flat surface,
then I go back to the beginning and start over cutting the cab.
usually going to a smaller size. since i usually am not cutting to a
calibrated size this make no difference to me. any slight stop in the
motion of the stone on the lap will cause you to have a flat spot. i
also cut my larger cabs without the dop stick and get better results.
oh the restarting is the rarity for me. but try cutting larger cabs
without the dop stick, just watch your finger tips.

john


#6

Hi Andrew.

I'm practicing making cabs using agate on a Inland Lapidary
Swaptop series, and I have a question about the hand cabbing
process on a stone mounted on a dowel with dop wax. 

This is kinda long.

Concerning the pits, that sounds like a material flaw rather than an
issue with your technique. If the material has pits, those will not
polish but if few and small you might be able to grind down past them
and then re-contour your stone and continue the grinding and
polishing. If more serious than that, it may not be worth the time to
try to cut a cab from the material.

I’ve done lots of cabs over the years but never on a flat lap so my
advice isn’t “tried” in your situation. I would think that contouring
and polishing on a flat surface would be more difficult than on my
Genie but I understand some people do use a flat lap like the Swaptop
for cabbing.

While you’re learning, I would suggest saving your larger (~40x30mm)
stones until you’ve cut a few smaller ones. A medium sized stone (say
nickle-sized) may be easier to manipulate and the job will progress
faster than with a large stone and you can track what is happening
and find what movements work better for you in shaping the stone.
Waiting to shape the very top of the stone with the second (325) lap
may be a good idea even if a bit slower.

Because the grinding is done on a flat surface, you will be creating
facets or flats on the stone but as you continue working around the
cab and eventually across the surface, you can knock down the high
points or ridges left from previous passes until the contour becomes
smooth. I usually continue working around the stone with each pass
focused on the ridge left at the sides of the flat spiraling "track"
I ground in the last pass. Those tracks will continue to become
narrower and the ridges less high and eventually the contour looks
more smooth than faceted. Then I’ll work across the stone from side
to side or end to end and all points in between until the contour is
even smoother and more refined. Of course there will be scratches all
over at this point but the next smaller grit will leave smaller
scratches - and so on until they are fine enough to finish by
polishing.

Along the way, check for flats by holding your wet stone under the
light and rotating and rocking it in all directions to see if the
light reflects from the cab surface evenly. Get your contour right
before switching to the 600 grit.

With each successive grit, work over the entire surface striving for
a smooth, even finish before changing to finer grit. If the entire
surface has been evenly worked, the next finer stage should proceed
without deep scratches or gouges appearing. The feel and sound of the
stone on the wheel will eventually become guidance as well.

Using the 10 power will show you the scratches for sure! Just don’t
let that keep you from seeing the bigger picture.

You will become better at shaping the cabs and will find whatever
rocking or swirling technique allows you to cover the entire surface
evenly while maintaining your contour. Then a close inspection with
good light and a magnifying lens should be adequate. I wear
magnifying glasses (+2) and use the 2 power lens on my Genie.

Hope this helps and good luck to you!

Pam

Pam Chott
www.songofthephoenix.com


#7
Hand sanding. In my 35 years of silversmithing and lapidary
experience, there is no way on earth to not 'facet' a cab on a
wheel. 

That was my first reaction, too, to reading that Andrew is using a
flat lap. Andrew, the flat laps are primarily for faceting a
gemstone. For doming a cab without “flats”, I think you’d have much
better luck on a wheel that resembles the Genie-type device.

No matter what device you end up using: don’t lean into the wheel,
let the grit do the work. And keep the stone moving at all times.

Lorraine


#8
I have to be able to completely get rid of all scratches, pits,
and lines for each grit as seen under 10X magnification, before I
dare go to the next grit. 

Yep, Andrew, and the harder the material the more it matters.
Somebody today said that you need to hand sand to get a clean cab,
which isn’t really true. You can hand sand as a way of getting past
your problem, true, but people make “perfect” cabs every day on
machines. A couple of strategies:

Use old sandpaper when it seems a good time for it. It is slower but
much less aggressive. Make sure you have padded sanding drums - not
hard laps but rubberized. And spinning the dop stick is a real art -
get on thewheel “in motion” so the stone is never stationary and
spin it ~fast~ with the right touch. Harder in the beginning and then
softer as it progresses. And agate can take a VERY long time to
polish - it could simply be that you are impatient.

I don’t know what you mean by “pits”. You should get no pits from
grinding and sanding unless your grinder is too rough for the
material, in whihc case it will grab and dig up chunks, leaving
pits. Or your material has some softer material imbedded in it. Or
Pits is the wrong word? Polishing anything is a process and an art,
and agate can be difficult and time consuming. It’s really just a
process of refining the surface little by little with finer and
finer grits - and a finer and finer technique, too.


#9

I’d keep the bevel edge at about 17-20 degrees for the first few 2-3
mm’s of height, then start the steeper curve. Otherwise your edge
might be too thin and might crack off when someone sets the stone.

Are you starting with a very clean lap, and using a copious amount
of water throughout? You need to keep debris flowing off the wheel.
(This is another reason why a genie-style grinder, especially the
CabKing with its entirely fresh water supply from above the wheels,
are good for grinding and polishing cabs.)

You might also identify unevenly rough areas on the lap – gouges,
striations – and avoid those.

I’ve never read Downing, but I don’t see how a cab after the 80-grit
wheel or 175-grit could possibly be even eye-clean, much less
scratch-free under 10x magnification. Are you sure he/she didn’t mean
that one should use the 10x magnification only at the end of the
entire process? Even a faceted gemstone may have a 10x-visible
scratch or two on one or two facets at the end of the process,
although one strives to polish those out.

I would say that after the first wheel, 80 or 175, the stone should
be covered entirely with uniform scratches, which the next wheel
replaces with smaller scratches, and the next with still smaller
uniform scratches, and so on, until at final polish no scratches are
visible to the naked eye. After final polish of an agate, you should
be able to read the reflected wattage markings from whatever lamp
you’re holding your stone under.

If you’d like to start over with new agate and a very clean lap, all
is not lost. You could facet that first stone all over its top with a
series of “flats”. The facets do not have to be mathematically
perfect meet-point style, because no light is likely to refract
through an agate anyway. All it needs to be is pleasing to you when
it’s finished.

Lorraine


#10

Your problem is using grinding wheels for the SANDING stages. I only
shape my stones using a 220 grit wheel and then do all the smoothing
using silicon carbide wet and dry discs mounted on a sorbothane
backing disc. This allows the sanding disc to distort and thus not
offer a flat surfce for the stone to abrade itself against. I
sand/smooth using 220, 400 600/800 then 1000/1200 grit discs.
Sometimes I may even use 2400 or 5000 grit discs for certain
materials such as malachite and lapis. For ruby and sapphire cabs I
use 220 diamond on copper wheel then diamond bonded to plastic discs
in 30, 15, 5, 3 and 1 micron, again on a pliable backing. The
plastic diamond discs are made by 3M and a couple of other companies.
I polish using felt, leather or various cloths such as silk, pellon,
rayon etc according to the stone. Felt and cerium oxide is my
commonest polishing combination. Your action for shaping seems fine
by the sounds of it. You will not get rid of all the flats with 220
sanding but the worst of them will go. After 400 grit sanding your
stone should be nice and smooth with very few flat spots and bad
scratches. After 600/800 sanding your stone should be smooth and
just dull, without blemishes visible to the naked eye

Nick Royal


#11

Hello Andrew,

Hate to tell you this but all you have done so far is reach the
’shaping’ stage. The next stage is sanding followed by pre-polishing
and finally the polishing stage.

Many cab cutters prefer a progression of grit size lapidary grade
silicon carbide sanding discs with foam rubber backing. I have great
success with Crystalite spin on pads and Diamond powder but although
much cheaper in the long run, the initial costs can be daunting. The
sanding stage takes the most time, is the most laborious and tedious
and also the single most important step.

Pre-polishing which is just very fine sanding, will take the smooth,
flat free, matt finish stone and produce a dull shine which clearly
shows any short comings in the sanding process. Going back to sanding
is the only choice, a prepolishing pad will just take too long.

Polishing is the most fun and also by far the quickest step. It
should be instantaneous in comparison to the other steps. If a
polish doesn’t occur in less than a minute then the pre-polish was
insufficient or the polish compound is inappropriate, Flats, dips,
and scratches can’t be polished out, but they can be shined enough
to really show themselves up.

If you can find a local rockhound lapidary club, seeing someone do
this will go a long way to understanding the process. Good luck.

Tony.
Anthony Lloyd-Rees.
www.TheGemDoctor.com
Vancouver,
Beautiful British Columbia.


#12

It is hard getting a good profile on a round stone using a flat lap.

A star lap(phenolic) has a curved surface and if you use a diamond
slurry or paste. Will most likely give you better results. Bombay
Bazaar carries them. Get several to run thru your grit sequence and
bag them(plainly marked) to avoid contamination. At all cost.

Best of all -not- pressing hard on the diamond flat lap and only
rocking the stone to get your initial rough shape. Might work
better?

If it’s pitting during polish? Cerium oxide on a felt buff will pull
any soft spots leaving a trench.

Some plume & moss agate have soft spots. Using a solid surface lap
(wood, phenolic, corian, plexiglass) and diamond 3000mesh to
50,000mesh will keep the surface integrity.

“Nova” vertical diamond wheels have a little give and will make your
work 100% easier. Find your local gem and mineral society or club.

Don’t stop=> just try something else.

James


#13

One thing to keep in mind is diamond discs when new are very
aggressive, but even when worn in they will grind a flat, part of the
trick is to lighten your touch as you refine your shape. This will
leave a smaller flat.

After 600 grit grinding (metal wheel) you should switch to sanding
on a softer surface, I like Nova wheels and they come in discs too.
I’d start sanding with 325 grit, then 600, then 1200. At this point
you can usually go to cerium on leather to polish though I’ve added a
3000 grit step in there.

Actually my usual progression for agates is 100 grit flat lap, then
I start sanding with the resin wheels, 275, 600, 1200, 3000, then
cerium on leather.

Fragile stones like opal, I might start with a worn 600 disc very
gently, then start sanding with 600

Agates are very tough and a good size cab can take (me) hours to
complete, especially the flat back sides. Many cutters rough the cabs
out to shape and tumble them to finish.

Practice and patience. I’m sure you’ll get many suggestions here.

Mark


#14
use a 600 wheel....is it a hard plate If so that is defeating your
efforts to smooth the surface. The next two or three stages should
be done on plates that have sponge rubber or cork backing 

There’s so much good advise on this thread today… Two fairly
important thoughts I’ll add just to be clear:

First is that all of the steps are important, but there’s kind of a
line of importance at 600 grit, and again, the harder the material
the more it matters. To a degree, 600 grit will cut through 220
scratches left from a bad 400 sanding (to a degree…) After 600
grit you just can’t do that anymore. Your stone MUST be perfect at
the 600 grit stage, IOW, or there is no hope of a good polish
further on.

In a nutshell, what you are doing is turning the surface into a maze
of finer and finer scratches, regulated by the grits you use. Even
tin oxide leaves a maze of scratches, they’re just so fine we call
it a good polish because they’re too tiny to see. In order to do
that you need to sand ~through~ the previous finish. People tend to
sand ~up to~ the previous finish and think it’s good. You need to
look through the 600 grit (for instance) and look for evidence of
400 underneath, and if there is any then you’re not done yet. Best
way to do that is on a dry stone, and the best way to get that is to
rub it on the palm of your hand…BTW…

You can polish a turquoise in 15 minutes, depending. Some agates of
the same size might take an hour or even more… Patience,
technique and the right tools all are key.


#15

Cabbing on a flat lap. This is the way I started, before I got an
used wheel cabber. You can do them fine, but you need a foam pad
under your fine grit disks. I didn’t glue my disks down to the hard
plastic foundation. Now, I have an Ameritool flat lap, but I am sure
the “swap top” is the same. I found that using the foam under the
diamond disk allows me to eliminate the flat spots and give a smooth
grind/polish. If you already glued them down, then good luck, I don’t
think you can do it.

Tom P
Heavy lifter for Designs by Suz


#16

I have to add a few comments:

When I took my first Lapidary Class, the instructor started everyone
on an Agate. Seems that Agate is probably the hardest stone to grind
to a wonderful polish and keeps the student busy for a looooong time.
That is the last time I have ever used an Agate to make a Cab! I
don’t need the aggravation. But it is sure one way to learn how to
use the series of grits!

I exclusively use an Ameritool Flat Lap and an old All You Need Flap
Lap from start to finish to do my Channel Inlay Bracelets, rings, and
donuts. It takes a lot of practice. I use mostly Lapis, Sugilite,
Black Jade, Petrified Palm, Dinosaur Bone, Turquoise, Jaspers, Coral,
and Variscite. There is a range here of hardness and can cause
undercuts if care is not taken. Soft touch is the answer!

I just learned from a member of a rock club how she uses the foam
pads under the final six polishing discs. I will be doing that with
the bracelet that I now have under construction of Leopard Jasper,
Black Jade, Petrified Palm and a touch of Gemmy Sugilite! I have a
private student learning the process and have to keep my demos ahead
of her so I can demo the grinding and polishing sequence.

I do have a vertical Ray Tech six wheel Lapidary Machine, but now
prefer the Flat Laps.

Have fun grinding and polishing…patience!
Rose Marie Christison


#17

Andrew, here’s the word from the president of Inland and developer
of the Swapto, Don Hirst:

Jim, there is NO WAY that you are going to "be able to completely
get rid of all scratches, pits, and lines for each grit" on any of
the grits. And, really that includes 1200G, 3000G, even further
down the micron scale. It doesn't matter what machine - horizontal
or vertical - you use. A 170G lap (or wheel) is gonna leave a lot of
scratches. Period. What I tell people is, you use the NEXT lap to
get rid of THESE scratches, ie, the 325G lap removes the scratches
put down by the 170G lap, and the 600G takes care of the 325G
scratches, etc. All will scratch, but you don't change laps until
you remove the LAST LAPs scratches... 

For what it’s worth, weteach our beginning lapidary classes using
the Inland machines - they’re good for basic cabbing. Graduates then
go on to vertical machines, right on through 14,000 mesh before
polishing. My ow preference is for using the Inland-type horizontal
wheels for shaping only, at 100, 220 and 325 mesh. Then I go to the
vertical wheels for 600 through 14,000 mesh sanding, and finally
polishing.

Hope this helps.
Jim Harkins
Blessed be…


#18

All,

I very much appreciate all the feedback I got for debugging my hand
cabbing process.

I made some experimental sanding sticks using wood, double-sided foam
tape, and wet-or-dry sandpaper, and the effect of those on my cabs
seems to be the equivalent of twice as fine as diamond laps of the
same documented grit. Eg: 600 grit wet-or-dry sandpaper stick seems
to polish equivalent to my 1200 diamond wheel but without the
additional problem of adding new facets.

So I did the following based on pooling everyone’s advice together.

Currently I have diamond plated 8 inch laps from Inland of the
following grits: 175, 325, 600, 1200, and 3000. The 185 and 325 laps
have been used but not very extensively, these have lots of bite
left. I used my 600 but not as often. I hardly use the 1200 and 3000
at all.

What I did today was machine half a dozen 8 inch laps out of Lexan
(acrylic plexiglass, rated 20 times the strength of glass).

I created a felt lap and 2 leather laps, using double sided Gorilla
carpet tape as my bonding agent.

I also created 400, 600, and 800 wet-or-dry sandpaper laps, using
double-sided foam tape as my bonding agent.

What I propose for my sequence for agate and jasper is as follows:

175 diamond: preform, rough bevel
325 diamond: fine bevel, rough rounding
600 diamond: rough sanding
400 foam backed wet-or-dry: fine sanding
600 foam backed wet-or-dry: initial prepolish
800 foam backed wet-or-dry: final pre-polish
leather, charged with 15,000 grit diamond paste: initial polish
leather, charged with 50,000 grit diamond paste: final polish

Would this be a satisfactory sequence, or would you add, delete, or
change anything based on my available supplies?

Thanks again,
Andrew Jonathan Fine


#19

Andrew, I believe you are making the process a bit more complicated
than it needs to be. After the first two diamond laps I would
recommend you go to a 280 soft plate followed by a 600 soft and a
1200 soft. Then you can either use a 14k/15k soft as a final polish
or got to the felt/leather and cerium oxide. You do not need the
50k…which is fine for faceting but not needed for cabs. As you
present it, you are doing too many unnecessary intermediate steps.
Also, in time I say you will probably move to all diamond and sans
the SiC.

Cheers, Don in SOFL


#20

Hi Andrew,

Your sequence sounds good, but I suppose it’s a very personal choice.
I’ve spent a lot of time and money figuring out what works great for
me. I only use 4 discs total to polish almost any material, whether
it’s opal or agate. You can adjust the pressure you apply and get a
lot of variation just using one disc. You should be spending the most
time on the first disc, with successfully less time on each disc. The
last disc should only take a minute if the previous steps are done
correctly.

180 grit hard diamond disk for preforming (although mine’s pretty
worn by now but I use this to rough out my shape completely) 600
grit silicon carbide or diamond-embedded resin disc, on sponge
backing (both are great for initial sanding, but resin lasts longer)
1200 grit silicon carbide or diamond-embedded disc, on sponge backing
(for final sanding/pre-polishing) 3M Trizact disc on sponge backing-
cerium oxide (white) for final polishing

Maybe others will say I’m crazy for only using 4 discs total but they
work great! The Trizact discs are amazing and much less messy than
leather. All of these run on water so it’s easy to swap out discs.
Like I said, if you vary the pressure on each disc, you can get quite
a variety of finish from just one disc.

Good luck!
Dana Evans