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Sparkie II - attaching nickel silver to copper

I recently purchased a used Sparkie II, and generally, have been
quite happy with it…until I attempted to attach (nickel silver)
stick pins to copper brooches. I can’t get them to attach
consistantly. Most of the time the discharge (80 v) is focused on
the underside of the fixture. I spoke with the manufacturer, and they
gave me some tips e.g. ensure that the pin’s base is centered in the
collet, and allow the pin to tip downward slightly so that the nib is
the first contact point. Still no luck. I’ve tried to analyze every
step of the procedure, but can’t find the problem. So, I’d love to
get some insight from other Sparkie II users.

Thanks much,
Ron Pascho

I've tried to analyze every step of the procedure, but can't find
the problem. So, I'd love to get some insight from other Sparkie II

Ron, the fixtures get a layer of oxide and grungy on their lower
surface after some use that reduces the contact between the fixture
and the piece. When that happens, the resistance between the piece
is equal to or greater than that of the contacting welding nib, and
you then get as much or more of a welding arc between the piece and
the fixture, rather than the finding. The solution is to remove the
fixture, and file or sand the surface back to being bright and clean
and smooth. That should help. Sometimes, a little bit of saliva on
the piece will help too. the moisture seems to improve the contact
between the fixture and the work, and then when the weld takes place,
the moisture in the weld area reduces the cleanup of "smoke"
required. It varies a lot from metal to metal, but give it a try.
Generally, the main things I’ve had trouble with, with the sparkies,
is in welding sterling findings to sterling silver. Sterling to
sterling welds have a tendancy to come out somewhat brittle, and it
sometimes takes a couple tries to get get a secure weld.
Interestingly, in laser welding, silver is also harder to weld than
other metals, not only because it takes higher settings, but also the
welds have the same tendancy to come out quite brittle and often
cracked, more so than most other metals. Those folks who’s lasers
are capable of pulse shaping have some means to correct this, but
earlier laser models without that feature, can be difficult to get
good welds on silver. I think in both cases it has to do with the
great thermal conductivity of silver, which means the welds cool down
much more quickly, which I think introduces greater stresses into the
cooling metal.