Joining Sheet Metal Together With A DIY Spot Welder

DIY Spot Welder

Once in a while there comes a time that you need a tool for one specific job. In these cases, it doesn’t make much sense to buy an expensive tool to use just once or twice. For most of us, Spot Welders would fall into this category. [mrjohngoh] had the need to join two pieces of sheet metal. Instead of purchasing a commercial unit, he set out to make his own spot welder.

spotwelder A spot welder works by passing an electric current through two thin pieces of metal. The resistance of the metal work pieces and the current passed though them creates enough heat to melt and join the two together at a single spot. To be able to get the high current needed for this project, [mrjohngoh] started with an old microwave transformer. He removed the standard secondary coil and re-wrapped it with 1cm thick wiring to get maximum current out of the transformer. The ends of the coil wire attach to electrodes, which are made from a high-current electrical plug. The electrodes are mounted at the ends of a pair of hinged arms. The weld is made when the two pieces of metal are sandwiched between the electrodes and power is applied.

Spot welding isn’t just for joining two pieces of sheet metal. It’s also used for things like welding tabs onto battery terminals. The versatility and easy of building these welders make them one of the most featured tool hack we’ve ever seen.

37 thoughts on “Joining Sheet Metal Together With A DIY Spot Welder

      1. You are not kidding check out these alarming facts I discovered about Dihydrogen Monoxide or as you call it water. Visit today and help ban this highly dangerous substance.

        1. That dihydrogen monoxide joke is so old it has fangs and can’t stand the daylight. You do realize it’s used to trivialize all kinds real, nontrivial dangers, right? Take a look at the LD50 for Tylenol sometime and tell me how comfortable you feel about chugging twelve of them a day for a week, which some people with severe pain will do if they don’t read the directions or don’t believe it because of stupid jokes like this.

        1. 94% . There have been about 110 billion people exposed to water over the history of Earth, and 7 billion of them (6.4%) are still alive.

          Therefore the death rate does not reach the standard P(.05) significance level required to show a statistically significant correlation.

  1. I don’t know if I would have the balls to use one I made, I am teaching myself electrical engineering not long started bought myself a multimeter along with lots of other little tools and components. Well I thought I would try and fix a laptop charger I had sitting around. I pulled out my trusty new multimeter and thought I can do this! So I opened up to power brick and started shoving the multimeter probes here there and everywhere. Then Bang!! a big Blue flash a deathening ring in my ears I Have never jumped so much in my life. I was walking back and fourth for a few minutes thinking about how stupid I was for just putting the probes on any componant without thinking. I live in UK so we have 240v mains I could have been toast.

    Since then I have a massive respect for electricity. I should have stuck with low voltage stuff until I had a basic understanding. Part of my problem was I thought multimeter’s where “perfectly safe” to use which I am sure they are when used properly.

    The moral of the story is nothing is safe in the wrong hands.

    1. I spent 15 years working as a commercial electrician, and I still have a healthy respect (aka slight nervousness) when dealing with mains power. It doesn’t matter if it’s 600v or only 120v, I treat it all with the same level of care and respect, which has probably saved my life more than once.

      I’m glad you weren’t hurt, but for the love of your own life, please don’t handle mains power unless you (meaning everyone) are properly trained to do so.

        1. 120V will absolutely kill a human if it passes from one hand, through your chest, and out through the other hand. The circuit breakers in most homes in the US on 120V circuits are 15A, and some are even 20A. The amount of current through your heart required to stop your heart is measured in milli-amps.

        2. Here in Australia there used to be a law that you couldn’t be a sparkie if you were left-handed do to the heart being on the left-hand side of your chest and the likelihood of grabbing something live with your left hand. Same went for colourblind people until they brought out the green and yellow earth wire.

        3. “120V will absolutely kill a human if it passes from one hand, through your chest, and out through the other hand.”

          Take a good multimeter and grab the leads in both hands. Then apply Ohm’s law.

          It’s 6 mA through the heart, 60 mA through the entire chest. My multimeter reads ~50 kOhm when I grab on to two screwdriver shafts connected to the probes. 120 V / 50,000 = 2.4 mA

          I would not be killed. I would be very very pissed off though. The main reason why you get killed from 120 V mains is because you can’t let go and you’re unable to breathe. It also causes internal burns which can lead to sepsis.

        4. 2 mA also happens to be the treshold of pain for humans. Below that, aside for the initial shock of getting shocked, you feel a kind of annoying buzz. The treshold of sensation is close to 1 mA.

          I have personal experience passing up to 5 mA at 40-50 Hz through various parts of myself from one of those electronic exercise machines, and I can attest that you are able to control yourself with some difficulty after you recover from the initial fright, and it’s not painful at all if the shock happens through a large contact area on the skin.

          Touching the electrode with your fingertip at 5 mA has the feeling of chewing a wet wool mitten with your front teeth, when the fabric slips against itself, except along the bones in your hand.

        5. Now put the multimeter probes on your tongue. That is the resistance of your insides. The resistance of the skin is higher when the skin is dry, and (might) save you, but it would be foolish to claim 120V mains cannot kill you due to lack of current through your heart.

    2. When multi-meters become too automatic, you must be able to predict what you will measure here. Or there, know what to expect.
      Measuring current is why they have separate terminal for the job.

    3. Oh, come on, of course care must be taken! I started working with electricity and 120 VAC at age 10. I knew 120 VAC was dangerous and had no mentor/elmer, so was always very careful. It was not until age 14 that I got shocked once poking around in an old pinball machine that was still plugged-in. I quickly let go and decided I did not want to get shocked again and continued working with electricity.

    1. Yes! I have done it. You do that by (obviously) making an electrode clamp setup with a fixed and movable electrode just like in the article, but you will attach your electrode holder and grounding clamp to this assembly. You will need to set the welder to it’s highest current setting. Then you will need to switch the primary of the welder on for the weld time you find is best for the spot weld you are doing (takes some experimentation).

      It does not work as well as a real spot welder. It is hard on the switch used to apply power to the primary on the welder, and can’t produce anywhere near as high a current. A real spot welder can momentarily provide 1000A currents. In this case you are limited by the maximum current rating of the arc welder. Definitely do not try it with one of those cheap “inverter” type welders. It would kill it pretty quick.

      I honestly don’t recommend it. But it works for thin gauge steels in a pinch.

  2. No one learns new things or makes new discoveries by playing by the rules. And if the first dude that tries something new dies- then we all learn something from that.

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