Scrap Yard Spot Welder

One of the prime user/buyer trades for the spot welder is galvanized sheet metal duct work.

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I just welded a couple of galvanized electrical boxes together- this thing is sweet.

Someday I'd like to have one of those. Saw a few at a recent auction, but they looked really rough. I picked up a few cool toys there, a hot knife for EPS foam for about $15, and a Speedflo paint sprayer with the separate motor for $15. A lot of the stuff at the auction should have gone directly in a dumpster, but there were a few guys there bidding their hearts out.

How long do the tips last? This thing looks like it has brand new tips on it, I'm still amazed someone brought it to the scrap metal yard.

Tips should last hundreds of welds in plain steel, perhaps half as many in galvanized. Tip life drops dramatically if you don't get a clean contact, oil on the surface, tips are misalligned, not enough pressure, sheets are warped, etc.

When the tips get all cruddy, you can file them flat with a standard mill file. After a few cleanups with the file the tip gets too wide. Then it's time to chuck them up in the lathe and resurface to get it back to the necessary diameter. I made up a holder that fits in the lathe, the tip screws in.

Be sure to take measurements >>I've done some pull testing of galvanized verus plain steel spot welding

Well, if it works, it works...

Dunno, I would assume the zinc stays more or less in the vicinity of the weld, so it might enter solution. I found a phase diagram and it shows good solubility of zinc in molten iron, so if it doesn't boil sideways away from the joint first, it will dissolve. On cooling I can't say what it'll do, I would presume the nearest intermetallic (gamma 1) is brittle, so depending on how much Zn stayed in the joint, it'll either be less ductile, perhaps stronger as a result; or simply brittle and weak. Annealing probably won't help, unless diffusion can spread it out, in which case a soak around 1500°F for a few hours may help to alleviate it. (FWIW, such a mixture may also be precipitation hardenable.)

If you do a short timed spotweld, you can also get a brazed joint instead. Probably more effective with some copper or brass in the joint, since zinc doesn't bond to iron very well. Not really any advantage, although it takes less energy and I would suspect tip life will be better.

Tim

-- "California is the breakfast state: fruits, nuts and flakes." Website:

Thanks. It seems to work very well on clean galvanized. Some electrical boxes welded together pretty well. WRT brazing, are you suggesting spot welding through a sandwich of steel/(copper or brass)/steel?

Yep. You ought to be able to put a small disc of thin copper or brass sheet/foil in the center of the joint. Such a technique doesn't sound familiar off the top of my head (although I do remember reading something about spot welded automotive connectors plated with silver and how it forms a brazed joint instead), but it should work. Again, mind that it doesn't take as much heat.

Tim

-- "California is the breakfast state: fruits, nuts and flakes." Website:

Do some checks for shorts to ground, etc. At places I have worked, if a tool goes bad, the first thing they do is to cut the plug off so no one will get hurt.

Pete Stanaitis

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ATP* wrote:

It wasn't cut off, it was unwired from something. I went back to the same dealer today and they had another one, similar but 120 volt, and the plug was still on that one. Bought that for $20 as well. I will check them both out carefully.

for the future, my opinion is that you could have gotten away with paying $10 instead of $20. In any case, you go a good bargain, even if they are parts units.

These guys take pretty good care of me, so I don't haggle if the price is right.