Back to Ganoksin | FAQ | Contact

Improving cabbing process


#1

Hi again,

I found something a little better than a magnifying glass and camera
to show one of my cabbing attempts.

Please find an attached 4800 dpi photo of one of my cabs. Dimensions
are about 12 millimeter across. If you download the photo and examine
it closely, you’ll see various flats and scratches.

I’d appreciate it very much if some experienced cabbers could examine
the this and make some suggestions about what I am doing wrong and
how I can fix this.

It is on: http://tinyurl.com/25tn7qj

Thanks,
Andrew Jonathan Fine


#2

Andrew, Those scratches are from your very first wheel (I guess that
would be the 175 hard disc right?). You are in too much of a hurry.
Slow down. By way of explanation. Sic is an abrasive but it will
break down into smaller and smaller grit as it is used against a
hard substance such as stones of 7 ( even less but it breaks down
more slowly). So as you cut with the Sic it will tend to remove some
of its own scratches (that we call ‘whiskers’) as the Sic particles
become smaller and more rounded. On the other hand, diamond IS
ALWAYS an abrasive and virtually each grit stays the same size and
each particle only slightly loses its sharp edges. Hard diamond
wheels lose their cutting effectiveness by the particles either
sloughing off or being covered by the metal of the wheel and
sometimes they become more embedded into the metal. As a result,
diamond will not ‘cover its tracks’ by smoothing over the initial
abrasive cuts. Depending on the coarseness of the grit, pressure
used, hardness of the material being cut, etc., these cuts can be
5-20 microns deep. The only way to remove them is to use another
diamond grit that is close to but still finer than the first one
used. For example, if you are doing your first grinding with a 175
grit diamond hard wheel/disc, you should probably go next to a 220
grit. Use high speed on the wheel and a light touch on the stone.
Move the stone very quickly in a circular motion and with each
revolution around the perimeter of the stone, tilt it slightly
towards the crown. After completing a cut from just above the girdle
to the crown, dry the stone and look at the surface with out
magnification. If you see ridges, gently turn the stone against the
wheel on that ridge. Dry and check again. Do this until you see no
significant ridges/flat spots (of course you cannot remove all the
ridges but they should be minor). More importantly, you should see no
’whiskers’ (short white lines like I see in your picture. Instead you
may see some much finer line or areas that have not lines.

Next you need to go to a soft wheel as I explained earlier…a
diamond pad such as a Crystal Pad backed by cork or sponge rubber.
Use a diamond paste (or powder mixed with olive oil for example) at
220 grit. (Don’t use too much paste…go lightly). Continue to use
high speed and medium pressure. Again, start at the girdle and work
towards the crown going in circles. You may want to sort of wobble
the stone a bit as you work up so you will break down any ridges that
remain. After a couple of times doing this, clean and dry the stone
again and look at it under a strong light (no magnification). By now
the stone should be perfectly shaped with a nice crown and good
geometry. There will still probably be a few of the fine lines but
they will not be deep and should be isolated.

Next use a similar wheel (Crystal Pad) with 600 grit diamond. By now
you might want to use a few drops of ‘extender fluid’ which is a
light lube that will keep the diamond particles suspended and active.
Use the same speed, medium pressure and the same process working up
the stone. After two or three times, wash and dry the stone and
inspect (without magnification). By now there should be no ridges or
lines visible and the shape of the stone should be perfect. The stone
should have a semi-gloss to it. Change to a similar pad with 1200
grit and do exactly the same movements, etc. When that is finished,
the stone will be pre-polished.

Now change to a wheel that has a felt pad on it. Use cerium oxide
that you keep damp. Do not get it wet or the stone will slide over it
and nothing will happen. If it becomes dry, the cerium powder will
bunch up and scratch the surface. Keep the wheel slightly damp use
slow speed, and as you press the stone down with heavy pressure until
the motor has to work but not so hard that it breaks off the stick.
Also don’t keep it on so long that it heats up and comes off the dop.
You might feel the wheel ‘tugging’ at the stone. That is perfect and
is the best polishing period. A few times over the stone and when you
clean it off it will be as shiny as possible. Now, if you wish, look
at it under magnification but don’t use 10x…its not necessary. The
human eye will not detect and scratches below 5 microns and should
appear perfect.

Stop with all the 3000., 4000, 8000 etc, etc. They are not needed.
If you use the above wheels, I guarantee you will have excellent
results on most stones. Now and then, if you are cutting something
like turquoise or malachite or even marble…the softer stones,
don’t use the coarse wheel…start with the 220grit. When you polish,
use ZAM on a cotton muslin buff as used in polishing metal.

I have been cutting for nearly 40 years and have cut thousands of
stones. Above is the general method I use…modified sometimes to fit
special situations. My advice though, is don’t try too hard and don’t
fight the stones. Just be firm and direct with the proper tools and
you will be successful every time (well, almost every time - there
are always some exceptions).

By the way, the above also applies even if you are using Sic wheels.
But there are slightly different speeds, pressures and hand
movements.

Cheers,
Don in SOFL


#3
It is on: http://tinyurl.com/25tn7qj 

I am not a member of facebook and was surprised when I couldn’t log
in. I guess everybody else must belong to facebook. But when you are
posting things for orchid members to see, I guess I just thought
you’d post them where everyone could see.


#4
some suggestions about what I am doing wrong and how I can fix
this. 

Jonathan, it’s completely obvious from you pic - you are impatient
(with the process). You have 220 grit scratches (whatever), ~under~
your finer sanding and what looks like the beginnings of a finish.
You MUST sand every step to completion. With silver you can remove
big scratches with a tripoli wheel - agate and other stones are so
hard that it’s simply not possible. 600 grit won’t remove 220
scratches in this lifetime, and 1200 grit never will. Each step must
be complete before you move on to the next - it’s not optional. And
if you do that with any reasonably proper equipment, the faceting
will go away along with the scratches, with a reasonable technique.
You just work it down - 220 is rough, 400 is more refined, 600 even
more so, etc.


#5

Andrew,

I think Wendell is right, you have scratches in earlier coarser grits
that you aren’t getting out. The finer grits won’t take care of the
deep scratches like one would hope. Finish each grit with a good even
surface (you will be able to see these scratches early on, get rid of
them then) before moving on. The harder the stone, the more important
this becomes.

I am no expert on rocks but this is what I have found to be true in
my playing with them.

Sarah Budde


#6
I am not a member of facebook and was surprised when I couldn't
log in. I guess everybody else must belong to facebook. But when
you are posting things for orchid members to see, I guess I just
thought you'd post them where everyone could see. 

You’re not the only one. I’ve resisted putting a page on Facebook for
a while now, after having some annoying things happen with a myspace
page. Yeah, it’s rare, but it’s made me lazy about joining. Just not
sure if it’s worth my time in real terms. I’ll admit my reticence is
wearing away, but so far, I’m not there either, and also couldn’t see
the photo. Not my loss, as far as I can tell. Posting things in an
accessable place is the posters responsibility, since it’s in their
interest to make it easy for viewers to get to. And there are many
places one can post photos on the web that do not force the viewer to
have an account or sign up…

Peter


#7

Andrew, Don is right. But is also has to do with the wrist motion. I
move my stones in a semi-circle. I will see if I can find my notes
from the classes I took at Modesto Jr. College and send them to you.

Veva


#8

The scratches are from not spending enough time on each grit. Use a
magnifying glass while you are grinding/sanding and check every now
and then to make sure that whatever scratches are on the stone are
all of the same size. Do not go to a finer grit until all the
scratches are uniform. The flat spots are from holding the stone
against the wheel without rotating it. Try to rotate the dop in your
fingers while grinding. This can take some time to get a good convex
surface. Harder materials will be more difficult. Sanding will work
better if you have a foam sanding drum to get rid of flat spots but
you will need to rotate the dop while sanding. Most important is not
to proceed to the next finer grit until each step is uniform. If you
leave a deep scratch from a coarser grit it is going to stay there
forever. It will just become a polished scratch. Take your time. You
will gain speed as you do more.


#9

Bericho,

I apologize. I did my best to make my cab picture visible to
everyone, but I’m not an expert in everything, try hard though I do
to be so.

Please give me your email and I will send you the photo offline.

Thanks,
Andrew Jonathan Fine


#10

All,

I read everyone’s advice up to this point and tried this:

I brought my steel diamond laps indoors without the Inland machine,
because I needed to learn the feel of the disks.

Then what I did was take the same agate that I posted on Facebook,
and resanded manually using the laps as “paper”, with PLENTY of
water. I started with my 175 grit lap, followed by my 320, 600, 1200
and 3000 grit laps. I followed that with 2000 grit 3M Wet-or-dry
paper, applied wet, to simulate a 4000 grit sanding.

I also followed someone else’s advice about coating my agate with a
Sharpie, then sanding the ink off with each wheel. I practiced using
my magnifying visor with its side loupe to search for scratches. I
also took 4800 dpi scans of the surface of the agate.

You’ll find the before and after salvage photo as:

Note complete absence of scratches with had been plaguing me before.

Lessons Learned:

  1. The ink exercise really works for building confidence with the
    laps. The amount of force necessary to remove the ink is just the
    right amount needed to also remove scratches. That tends to be a very
    light touch.

  2. So long as that above light touch is taken, the smoothing laps
    that people have advised me to buy are not strictly necessary. When I
    have the money, I can then buy them to make it easier to prevent
    flats, but the ink exercise taught me how to use just the right
    amount of force to prevent them also.

  3. I found it easier to hold the flat lap in my left hand and the
    agate in my right, so as to be able to view where the spots of ink
    remaining were. (I had such trouble with being able to see where I
    was grinding using the machine, that I am now seriously tempted to
    mount my flat lap machine at right angles on a wall using screws, and
    then drip water on the wheel with a pump!!!)

  4. On the other hand, steel diamond wheels are not needed for
    sanding after the doming is finished, even if they would be helpful
    and faster. I could just as well go indoors and use diamond paper on
    wood blocks.

Thank you all so far for your help in my progress thus far,

Andrew Jonathan Fine

(Yes, I know it’s Facebook, and I’m sorry for that. It’s the only
place I found where I can post unlimited photos of unlimited size for
free.)