Re:Re: ATM alternative grinding materials

["Dennis Nikitin" <ndenis@sarkor.com>]

----- Original Message -----
From: Anthony Stillman <atmer@flash.net>
To: Dennis Nikitin <ndenis@sarkor.com>
Cc: <atmer@flash.net>
Sent: Wednesday, December 26, 2001 3:53 PM
Subject: Re: ATM alternative grinding materials


> Good luck.  Please post your progress.  I've always wanted to work a
mirror
> start to finish just using the grit with which I started.  Washed,
> re-washed, settled and re-settled.  Well, maybe one of these days.

Hi, Anthony

Thak you for informative response.
Actually settling is what I allways do. I've been allways doomed to
economize each particle of grit!  It's ok but have some specific moments.
Here is my report.

It's ok to reuse grit but as far as you can sieve it using a fine screen.
The microgrit obtained by settling is a mixture of the grit itself and the
crushed glass. When you settle this mixture the grit particle sink faster
then  the glass one because they have different dencity. Normaly glass
dencity is 2.5 gramm/cm3, artificial alum. oxide - 3.2 gramm/cm3, natural
alum. oxide - 4 gramm/cm3, silicone carbide - 3.2 gramm/cm3. They sink with
different velocity, here is the exact formula. You can calculate time to
wait to get grit size you want.

V = 6000(R-1)d^2,

V, cm/sec - velosity of sinking particle.
R, gramm/cm3 - dencity of a particle.
d, cm - size of particle, must be multiplied by itself in formula.

Important!You should use units of measurement as is - no inches.

Thus you can see that  the mixture which is suspended at a moment contain
particles  of grit of certain size and particles of glass which are 1.5 - 2
 biger. They will cause SCRATCHES (many many of fine and mean cratches
)   )  during the fine grinding. There is no simple method to remove glass.

So you should prepare microgrits for fine grindig separately. Crush it
between two steel discs and then settle but before... The mixture will
contain steel particles,  not many of them as steel is at least 20 times
more endurable then glass. Also it is easy to remove steel particles by
holding grit in 20% sulphur acid solution. Leave it for a day or so, than
whash the grit of acid. Note that the mixture must be suspended permanently
to let the acid reach every particle. I used a small DC motor and a
propeller of a toy boat.

The next method is much more clean. I used powerfull permanent magnet of an
audio speaker. Suspend the magnet in a pot, add water and mixture, aply
motor+propeller. Wait for a few hours to be shure.

Let me know if you'll try it. I would like to know if my way is
reproducable.

Good luck,
Dennis Nikitin,
Tashkent, Uzbekistan