[Rockhounds] sphere-makers: how do you make very tiny spheres?

[Jim Murowchick]

Don-
    I made some very small pyrite spheres to use as seed crystals for some
crystal growth work back in 1980 or so.  I'll see if I can describe it, but
let me know if you want a sketch.
    The body of the grinder was a ca. 2" x 2" x 1/4" thick slab of something
(it might have been steel or aluminium, or ceramic--I can't remember) with a
1 to 1 1/4" hole drilled through the sides.  A small (maybe 1/16' inch) hole
came in from one edge so that compressed air could enter the chamber
tangentially.  A small brass or copper tube extending out from the hole
allowed some plastic tubing to be attached for the air.  The sides of the
chamber were covered with a flat plate with a small (ca. 1/4" hole in the
center of each side.  The hole is covered with a fine mesh on the outside
face so the air can escape, but not the bead.  The plates are held against
the body with a couple of those black spring clips.  I don't remember if
there was some sort of gasket under the plates for a better seal.  If
needed, a simple O-ring larger than the chamber diameter would work.
    The cylindrical face in the chamber is lined with a layer of wet/dry
abrasive paper, glued with rubber cement to the chamber face.  If a polish
is needed, you might need to use successively finer grits.  I don't know if
a high polish can be obtained or not--we needed a sphere with a smooth, but
not polished surface.
    A small piece of your material is put into the chamber, which is then
closed up.  Start the compressed air, and the sample will whizz (that's a
technical term) around and around, becoming rounded in the process.  The
dust escapes out the sides.  For the work I did, it took less than a minute
to make a pyrite sphere about 1mm in diameter.
    With a little experimentation with grits and air flow, and grinding
time, I think you'll get what you need.  You might need to immerse the
sphere in a refractive index oil for optical work if the polish is not good.
    I think the device is described in a back issue of American
Mineralogist--I'll see if I can track it down.

Cheers,
Jim


On 3/14/09 4:16 PM, "DonH" <donhalterman at verizon.net> wrote:

> 
> Hi,
> 
> I know some of you make spheres, usually of the 1/2" to 6" (or whatever)
> variety.  I know how these are made and have seen the equiment.
> 
> However, is anyone familiar with making extremely tiny spheres, less
> than 1 millimeter in size?  I would imagine the milling process as I
> know it doesn't scale down that small.
> 
> Thanks,
> Don
> 
>