On Fri, 23 Apr 2004 08:01:43 -0400, "Backlash"
wrote:

Spotwelders can actually be pretty simple. An appropriate transformer,
timing device, relay to control transformer primary supply, and mechanical
clamping of the tips are what are required. We have several shop built
spotwelders at work to weld smaller parts. I have a 15 KVA commercial unit
at home. To weld sheet metal body parts, I think you'll need transformer
ratings of about 5 to 15 KVA. The electrical expert types will have to be
the ones to determine this. I use 15 KVA units to weld 1/16" steel tubings
telescoped together on a setting of 3 of an available 5 on the range
selector of a factory built unit. Water cooled tips are used for production
work. A capacitive discharge unit is what I use to spotweld brass to bronze,
and brass to stainless. Spotwelding basically is a process of mechanical
clamping pressure at the tips, electrical power applied through the tips,
holding time for this power, then release of clamping. All of these
variables are adjusted for weld quality of the "nugget". Special coppers are
required, and tip diameter is important. A company called New Southern
Resistance Welding is where I get my basic supplies. Miller makes a handheld
unit for body panels. Maybe you could copy it's design. Hope this helps you
a little.

RJ
A couple years ago I made some screens for a customer that consisted
of a brass frame with brass chicken wire. The frame was silver
soldered at the corners and the screen was soft soldered to the frame.
I wanted to spot weld the screen but Miller said it was impossible.
Now, I read your post about doing something similar. Did you build the
capacitive discharge unit yourself? If so, would you supply
schematics?
Thank You,
Eric R Snow