Home Brew Spot Welder

Anybody here ever built your own spot welder? I've got some major re-assembly work coming up on my jeep tub & I've been thinking it
might be easier/faster to do real spot welds instead of the "drill hole/mig weld plug/grind down" route. I've found a few references on google to plans for units using re-wound microwave oven transformers, intended for use on small projects such as model gas turbines, but there isn't enough detail to convince me they'd work on heavier sheet metal.
So, if you have any experience with something like this or know of any on-line resources that google (Gasp!) doesn't know about I'd appreaciate hearing from you.
Thanks,
Howard.
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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
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"Howard Eisenhauer" < snipped-for-privacy@REMOVECAPShfx.eastlink.ca> wrote in message
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wrote:

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
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Eric, The capacitive discharge unit is a factory built unit. I drug it out of a storage barn at work and put it into action about 10 years ago. It uses vacuum tube technology to load and discharge a bank of caps through the tips. I can get the model number and such if you want, but I'm pretty sure it's now considered obsolete. I had a similar experience to yours. I needed to externally swage some .065 stainless steel tubing with a .002 wall thickness down to .035 thousandths for a length of 1/8". Torrington Swager Co no-quoted the tooling and said they wouldn't touch the job. I took two small blocks of tool steel, clamped them in the mill vise, and drilled a hole on the parting line of the blocks. Deburred with a beadblaster, hardened them, polished the bore, and installed them and went to swaging. They are theoretically supposed to have all kinds of reliefs ground into these type blocks to make them work, but these have been turning out thousands of parts a year for about 10 years. Reality versus perception, I guess.
RJ
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wrote:

Well, thanks anyway. Guess I'll look into this type of spot welder and see if I can build one. ERS
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Jewlers use little versions for welding posts on to ear ring bodies jk
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Eric,
You may give this a try: http://www.5bears.com/theshop.htm
This chap has some very nifty projects.
Cheers, Norman
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http://www.metalworking.com/dropbox/_2002_retired_files / See welder00.txt and the associated jpgs. JR Dweller in the cellar Howard Eisenhauer wrote:

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JR North wrote in message news:

I fooled around with microwave transformers, i made it work, but not well enough to do body work, worked quite well on stainless steel though.
while i was fooling around some one called around and when he saw what i was doing offered me an old handheld spot welder. It's magic, not at all fancy no timer or ajustment. you just clamp it and give the trigger a squeeze, you hear a click and the weld is done...
the bloke I got it off used to use long arms in it and was able to do all the spot welds in a mini body shell, i gather he needed a helper to hold it as the whole thing got a bit awkward to use....
I would buy one secondhand and sell it when your finished, probably won't cost you anything in the long run and it should work fine.
-- richard
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Thanks Jason, a couple of questions:
How did you determine the number of secondary windings required?
Will your unit handle 18 gu. steel without suffering a meltdown?
Did you try differnt combinations of series/parrallel on the transformer windings to find what works best?
Thanks again,
Howard.
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3 turns gave 12V open circuit. The phasing on the schematic gave the highest saturation. Other schemes did not work well. It is quite powerful. It can weld 20GA SS with .2 sec setting, and 16 GA mild steel with .5 sec. I have run 1 sec welds, without popping the 30A line breaker. This will melt through 16 GA and weld the tips together. JR Dweller in the cellar
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