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This list digest contains the following message subjects:

1. LapDigest Issue No. 124 - TUES 3/10/98
2. NEW: Setting Up A Lortone Beaver Arbor
3. RE: Eliminating Flats
4. RE: Eliminating Flats
5. RE: Eliminating Flats
6. RE: Eliminating Flats
7. RE: Eliminating Flats
8. RE: Eliminating Flats
9. NEW: Eliminating Flats
10. RE: Eliminating Flats
11. RE: Eliminating Flats
12. RE: Searching for Material for an Eagle's Eye
13. RE: Another Motor question


Subject: LapDigest Issue No. 124 - TUES 3/10/98

Since the last issue was published (yesterday), the Digest
has received 13 replies, so I am doing a new issue before the
next issue gets too big!

Our co-member and friend Mel Albright always ends his
correspondence with the following advice: "Hug or call
someone you love today!" ...and it is good advice!


Subject: NEW: Setting Up A Lortone Beaver Arbor

I need suggestions for setting up my Lortone Beaver arbor.
I'd like to keep the 100 and 220 Silicon Carbide wheels but
was mainly concerned about the 2 drums (foam backed, not
really true expanding drums) and the left most flat disc and
the right most flat disc. I'd be willing to go with diamond
(especially on the 'inner' drum as it will be difficult to
change) but am not sure if, say, 600 then say, 3000 on the
drums is workable or not. If a 600 diamond cuts almost as
fast as 220 SC then perhaps 800-1200 next?

I realize the material I'll be cutting has a bearing but if
I set up the inner drum for agates I have the option of
skipping it for, say, obsidian or whatever. Anybody have a
mixed setup like this?

1 Lucky Texan

Non-commercial reprint permission granted

Subject: RE: Eliminating Flats

Derek Morton wrote:<snip>

<<Grinding and shaping go very smoothly. Now here is the
problem: no matter what I do, I can't eliminate all the flats
before polishing. As I move from 100 to 320 to 600 the larger
flats are simply replaced by a larger number of smaller flats,
no matter how many different ways I rotate the stone against
the wheel and no matter whether with a light touch or with a
lot of pressure. It seems like maybe the 8" wheels are
producing a surface speed in excess of what is needed for
such small size cabs. The cutting action seems too fast and
the drum does not "give" like I think it should. Am I
missing something here? Do I need to go to 6" drums or
possibly Nova wheels? <snip>>>


I have found that in my case a lot of my flats are caused not
by my equipment, but by lack of education in my hand. By
watching closer and smoothing out the speed and roll of my
hand motion on the courser grits a lot of the flats went

Hang in there.
Craig Nielson

Subject: RE: Eliminating Flats

I believe that your shaft speed is too high. The higher the
speed the 'harder' the drum becomes.


Subject: RE: Eliminating Flats


Diamond Pacific makes two sizes diamond impregnated pressed
rubber wheels about 1/2" thick, and slightly convex. This
expressly for your purpose! Sold in sets of 4 to 14,000 I

As a side line, I produce extraordinary beautiful stones as
free forms by tumbling. Not your run of the mill stuff-
plumes, mosses, picture jaspers etc. If interested, our URL


Subject: RE: Eliminating Flats

IMHO, Nova wheels will completely eliminate this problem. I
had an identical problem with my Carborundum arbor and found
out it was the expandable rubber drums. The rubber was old
and too hard to give enough. New drums eliminated the problem
but I have since switched to a Titan and love the Nova wheels
so much it's hard to imagine going back to slow silicon
carbide belts. The Nova wheels give much more than any rubber
drum I have used and since switching to them my stones are
much more perfect in overall shape and smoothness.

Tim Fisher /
Ore-Rock-On and Pacific Fishery Biologists WWW Sites:
See naked fish and rocks!

Subject: RE: Eliminating Flats

Sounds to me like you have some very "new" sanding belts.

If this is the case, use a piece of scrap agate to wear in
the belt so that it doesn't cut so fast.

The other possibility is too many RPM. If you have step
pulleys on your set-up go to a smaller size on the motor,
larger on the spindle.


non-commercial reprint permission granted

Subject: RE: Eliminating Flats

I also make a lot of free form pendants, and I ran into the
same problem you did: getting rid of flat spots. I started
out using diamond grinding and polishing belts on expanding
drums, and unless the free form pendants were domed or
rounded, I inevitably had flat spots on the pendants, usually
right in the middle of the pendant where the diamond belts
did not make enough contact. I was advised by my mentor to
switch to nova wheels instead of the diamond belts, since the
very outer edge of the wheels can be used to reach the
interior parts of the pendants. I tried them out, and it
solved my problem immediately.

I polish the free form pendants by holding them in my hand,
rather than dopping them, but you can do it either way. When
you need to polish the very interior of a pendant, you can
hold it at an angle to the edge of the nova wheel and let the
last 1/8 of an inch of the wheel's edge flow across the
center of the pendant. It will seem like the edge of the
wheel is touching the center of the pendant in a totally flat
manner, but there is enough diamond in the rubber-like
substance of the wheel, and the edge is firm enough that this
contact with the pendant will actually polish it. Remember
that the wheels need a breaking in period, and the first few
pendants will be polished in the center, but may appear to
have minute ripples across the surface. This quickly
disappears after the wheels break in, and then you will be
able to do several hundred pendants (or more) before the
wheels ever have to be replaced.

There are other reasons why you may have flat spots,
including not using enough water lubrication on some
materials, lingering on one part of the pendant too long, or
using too much pressure. Those mistakes have other remedies
of course, but if the problem is that you just can't reach
the interior portions of your pendants, then the nova wheels
will help.
Vance McCollum

Subject: NEW: Eliminating Flats

Have you checked to make sure that the arbors are true and
that the wheels are centered??

If you're using belts on an expandable drum, is the expansion
joint smooth, maybe its is out of alignment.

Your problem sounds like you are getting a chatter of some
sort, which causes what is commonly called "Orange Peel", or
flat spots. A wobble of any type will cause the problem you

Gil Shea

*****non commercial reprint permission granted*****



Subject: RE: Eliminating Flats

Hi Derek,

Although I have only a couple of years experience in lapidary
it seems to me that you may be missing a step in 'sanding'.
The shop where I do all my work goes from #80 to #180 to #280
then #400 and #600. I know that almost all of the little
flat areas disappear if I spend enough time on the #280
wheel. If I don't spend enough time there and haven't spotted
the pernicious little flats, they will sure show up when I
go to the #400 and #600 wheels.

Hope this helps.

Tom Burchard

Subject: RE: Eliminating Flats

Hi Derek
Flats are not caused by the size or type of your expandable
drums. Flats are caused by not keeping the stone moving in a
sweeping action across the grinding surface. I prefer to
sweep the stone from the center to the edge except in stones
that are easily chipped and then I reverse the direction. You
should not have any noticeable flat spots at the completion of
the sanding stage. The prepolish should be to remove the
minute surface scratches prior to polishing. Remember, your
polish is going to be only as good as your prepolish.

You didn't state whether your machine is homemade or factory
built. If you made your own check your shaft speed. An
expandable drum becomes more rigid the faster it turns. I
prefer a shaft speed of about 1000 rpm for 8" drums. If your
motor pulley and shaft pulley are the same speed , you are
probably running too fast. The formula for RPM is: Motor
pulley diameter divided by the shaft pulley diameter times
the motor speed equals shaft speed.

Also consider going to a hard silicon carbide or diamond
wheel for your course grit. It's faster and cheaper in the
long run.

Hopes this helps


*****non commercial reprint permission granted*****

Subject: RE: Searching for Material for an Eagle's Eye

Here are 3 more unlikely candidates:

1. The center of a 'pyrite sun'. Although I never see really
small ones, you actually only need the center 1/2 inch or
less right? Maybe a broken one would be cheap. I have also
seen some pyrite 'cylinders' which could be sawn into discs.

2. Petoskey stone. probably not the right color though.

3. Fossil coral or limb cast. Again, color is the problem.
Have also seen 'coprolite' with largish spots.

1 Lucky Texan

Non-commercial reprint permission granted

Subject: RE: Another Motor question

Another problem which occurs on electric motors is that the
"Brushes" wear out. If that happens the motor won't work
either. Brushes are also the easiest and cheapest part of
the motor to fix (usually).

Gil Shea

"non-commercial republishing permission granted"
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