Making a tool cavity

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?
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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
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Wow. I think maybe you are making it more difficult than it needs to be. The normal way to get that nice shiny half dome end on a chunk of fiber optic rod in a gun sight is with a butane lighter. Slip a chunk of rod through the hole. Leave about one diameter sticking out. Less for a smaller diameter end, more for a larger one. Wave the flame of a lighter at it. It will melt into that perfect half globe of plastic. No polishing required. If you want to make up a few with one end done for spares, just drill an appropriate hole on a scrap of aluminum. I use 1.5mm fiber optic for front pistol sights. A 1/16" hole is just right.
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Bill Marrs
Must be you get cleaner burning butane than I do, any time I use a butane lighter or midget torch on plastic for polishing purposes, I end up with soot embedded. On the other hand, I do have a nifty hot-air tip for one of my butane soldering irons, I might just try that out if I can dig it out from where the tool monster has it hid.
The inserts don't get busted in use so I don't need spares, red is absolutely useless for a sight color for me and that's what most fiber optic sights come with. So I've been busy converting them to green, which works better.
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There is a bit of technique involved. It's especially fun when you are doing it between stages at an IPSC match, standing in the rain with the wind blowing. I do bust a few in use, usually by getting too close to a port or barricade and whacking the front sight from recoil. There is a discussion on fiber optic sights going on now over at
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Some good info there. I've tried both the red and green. Either one works for me, but I trend toward red.
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Bill Marrs
I was getting it from Lees Red Ramps
"A prudent man foresees the difficulties ahead and prepares for them; the simpleton goes blindly on and suffers the consequences." - Proverbs 22:3
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