If you’re making a LOT of them, you might wish to make a jig. Find
(on ebay, or elsewhere) a chunk of graphite block as thick or thicker
than the total final length of the head pin you wish to make. Drill a
hole that’s a somewhat loose fit for your wire to the depth of the
wire portion of the headpin, and use a ball bur or cone bur or
something of the sort to bevel the top edge of the hole. not a lot,
but so the countersink is almost the size of the ball you’ll want.
To use, cut your wire to the length you’ve determined is
appropriate, and drop it in the hole so a bit sticks up. Graphite is
an exceptionally good heat sink, and will keep the length of wire
that’s IN the hole, virtually cold, or at least, not much warmer than
the graphite block itself. Put a tiny bit of flux at the tip of the
wire before putting the wire into the hole. You’ll then need a torch
with a good hot flame (oxygen/fuel, not just a plain propane or
blazer torch). Because the graphite is a heat sink, you’ll need a
flame hotter than you might expect. Point it straight down at the end
of the wire, towards the graphite block. If you’re using the right
flame, the end of the wire will ball up almost instantly, dropping
down to not quite touch the graphite, and the ball will remain
centered by that countersink you cut. It will chill almost instantly
when you remove the flame, and you simply pull the resulting headpin
from the block (use tweezers, 'cause the block will become too hot to
hold in your hand after a few of these), and do the next. try to
avoid flux on the graphite block itself, as that will gum things up
and glue the pins to the block. So apply the flux to the tip of the
wire before dropping it into the jig.
You can also make such a jig from considerably thinner graphite
sheet. I’ve made them from 1/4 inch thick graphite sheet. This allows
you to make any length of pin you wish, but then you’ve got to hold
it in some sort of third hand or other arrangement, so the length of
wire is determined by what the wire hits underneath the graphite.
Graphite is a bit slippery to hold in tweezers, so getting this set
up to work can take a bit of jerry rigging. But the thinner graphite
is cheaper to buy, and the end result is just as good.
The beveled hole edges eventually get a bit too burned, and then you
simply drill another hole a quarter inch away. Or with the thinner
graphite sheet, flip it over and use the other side.
I was recently doing something similar, smaller balled ends than
most headpins, on short gold wires for nose studs. Because I was
balling up the end of the wire after a bezel had been soldered to the
other end, a simple hole wouldn’t work. So instead, a fairly tightly
fitting slot in an edge of graphite sheet, also beveled to a slight
cone at it’s inside end, did the same thing. With that, the wire was
slid into the slot from the side, and the thickness of the sheet of
graphite also regulated the length of the finished stud. After
balling up the end, it could simply be slipped back out the slot. The
slot was made to a snug fit so friction would hold the wire in place
while being balled up. That was an order of over a hundred pieces
like that, and by the end, the graphite was just beginning to show
some heat effects, but had a lot of use still ahead before it would
need to be remade.
Hope that helps.