Weld nuts:
http://www.on-b.com/doc/onb-nut.htm
All sorts of flavors but they do a nice job of adding threaded holes and
studs to sheet metal types of assemblies. The projections on the weld
nut provide a focal point for the heating.

Typical weld heat requirements here
http://www.on-b.com/weld/wd-lc-nu.htm


Bob Engelhardt wrote:
RoyJ wrote:
If you are doing a simple 1.5kw or 2.5 kw unit for sheet metal work,
the "pull the trigger and watch" is just fine.

I have 2 microwave oven transformers, from ovens that were rated about
1.4kva each. I plan to measure my actual power in, but I expect that it
will be about 2.5 kva.

We did some testing on 20ga
steel with a 1.5kva Miller and a tensile tester, the sweet spot in
timing (short, medium, long) is quite broad. In our case it was fine
from about 2 seconds to 4 seconds IIRC. Too short results in poor
strength, too long results in rapid wear on the tips.

Ah, good to know.

Galvanized stock
is a different story, the time to burn off the zinc is significant but
also adds a lot of variability to the individual welds.

Yeah, I expect that the zinc burning off would be a loose cannon in the
process.

When you get to thicker stock or weld nuts, you will want to have a
pulsed sequence that allows proper heat flow in the weld area. When
you buy the weld nuts, the manufacturer will specify a recommended
sequence.

Though I don't know what a weld nut is, I probably won't be using them.
The welder is really for sheet no thicker than 18 ga, 16 maybe. Thicker
than that will be MIG time, or stick.

Thanks for the input,
Bob