This spot welder I'm building: does it need a timer, or can I use it "by
feel"? I.e., pull the trigger 'till it looks done. IOW, how crucial is
the timing?

Thanks,
Bob

Bob Engelhardt wrote:
This spot welder I'm building: does it need a timer, or can I use it "by
feel"? I.e., pull the trigger 'till it looks done. IOW, how crucial is
the timing?

Thanks,
Bob

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. 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. 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.

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.

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

On Aug 31, 4:45 pm, Bob Engelhardt wrote:

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

There are special nuts with projections on the bottom that are made
for use with spot welders. The projections make it so that there are
only three relatively small areas that contact the sheet metal. So
you essentially get three spot welds per nut. Your welder would
probably do just fine with them. But you won't find them at the local
hardware store.


Dan

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

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.

The other problem with spot welding galvanised it that the zinc alloys
with the copper at the electrode tip reducing its perfomance and
requiring more frequent dressing of the tip.


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

On Aug 31, 6:45 pm, Bob Engelhardt wrote:
RoyJ wrote:

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.

Weld nuts are pretty much what they sound like. There nuts that are
designed to be welded onto sheet metal to create attachment points.
The ones I've seen are round (cheaper to form) with 2 points that
stick out to assist in alignment (the sheet metal will have dimples
stamped into it).

RoyJ wrote:
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.

Those are neat, they could be handy, except ...

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

20kva minimum!

Although I don't see how it would be much harder than the 2 1/8" pieces
I welded together.

Bob

David Billington wrote:
The other problem with spot welding galvanised it that the zinc alloys
with the copper at the electrode tip reducing its perfomance and
requiring more frequent dressing of the tip.

Good to know. All told, galvanized is probably something that I'll
avoid with the spot welder.

Bob

Bob Engelhardt wrote:
This spot welder I'm building: does it need a timer, or can I use it "by
feel"? I.e., pull the trigger 'till it looks done. IOW, how crucial is
the timing?

Thanks,
Bob


I'd like to have a coin slot on mine. Grad students are always coming in
to use it.
Randy