You may want to try this, but it does require that your sphere is
very round. After you’ve done your initial clean up with a coarse
file, put the bead aside.
Make a mandrel from sterling silver. I have a mandrel that is made
from solid wire, just over 4.2 mm but you can also use tubing if you
have it or want to buy some. If you’re using solid wire take a large
round bur and cut into the end. Cut deep enough so only the very edge
of the mandrel comes in contact with the sphere.
Using the least amount of solder possible solder the mandrel onto
the sphere. Normally when I make a sphere I fuse the halves together
so there’s no problem soldering the bead onto the mandrel. If you
solder the halves together make sure you use the hardest solder you
can. When soldering the mandrel onto the bead use the softest silver
solder you have. Solder the bead onto the mandrel only after you have
drilled at least one hole into the sphere for hot gas to escape.
Soldering a closed hollow object is extremely dangerous and puts your
safety at risk; It also could destroy all the work you’ve done to
Normally I solder the bead over the spot where one of the holes will
go. Let’s say for sake of visualization that the holes are at the
north and/or south pole of the bead. Don’t place the seam at the
equator, but offset from it. Don’t cover the seam with the mandrel.
Now place the prefiled bead in a rotary headpiece. Make sure the
bead is close to the headpiece. If a lot of the mandrel is showing
the mandrel could easily bend if the bead gets too much pressure
placed on it at a too high rate of speed. So, always use the slowest
speed you can and the least amount of pressure necessary. Once the
bead is mounted in the headpiece, slowly rotate it. Make sure that it
is turning true. Sometimes you can bend the mandrel a bit to make it
turn more true, but the best thing is to have a very round bead set
perfectly on the mandrel.
From here I would take some 180 grit sandpaper and hold it against
the bead. Experiment a bit. Sometimes I use the sandpaper on a stick,
but I always end up holding the sandpaper against the bead by hand.
Remove only enough metal to get below the file marks, them move
quickly to higher grits of paper.
Once you’ve achieved the sanded finish you desire, take a saw and
cut the mandrel off as close to the bead as possible. I usually hold
the bead against the sawblade and slowly cut the mandrel until it’s
nearly cut through. I hand cut the rest of the way. Here you will
need to file and sand the remaining part of the mandrel and the
solder off the bead, but if it is near where the hole will be
drilled, or in an area away from the equator of the sphere,
distortion will be visually minimal.
Remember to always file and sand in a flowing motion across the
surface. If your wrist is locked and you are filing facets into the
surface you’ll always have distortions.