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wrote:
I have need, from time to time, to replace small plastic fiberoptic
rods used for gun sights. The factory rods have a small rivet-type
head on each end of the rod for retention. Mulling it over, I figure
that maybe using friction and spinning the head on would work. To do
that, I'd need a highly polished spherical cavity on my spinner. I've
not had great success producing same in the past, this would be
probably between 2 and 4mm across. I've come up with a methodology
that will probably work. I'd either make up a D-bit with a
hemispherical end of the proper radius(probably 3-4x the radius of the
fiberoptic rod) or use a carbide burr in a micro die grinder/Foredom
handpiece to produce the shallow cavity in the end of the tool. I'd
then use a tungsten carbide ball and use that in conjunction with a
bench vise or press to produce the surface finsh I want. Lee uses
something similar to produce lead ball molds for blackpowder shooting.
I'm considering using something like 1/4" brass/bronze rod that I've
got sitting around for tool stock and using a pneumatic micro die
grinder for driving the tool after it's made becuase it can be
throttled way down. If I end up making up an alignment jig, it's would
be simple to use a V-block mount on the cylindrical die grinder body to
mount it to the jig. Anybody ever done something similar?

Stan

Stan, look at some of the jewelry supply websites and look for a dapping
die. They are a series of graduated semi-sperical depressions used to
make 1/2 of a bead or a domed form in non-ferrous metals.Some can be had
for a cheap price.
Michael