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