Joining Sheet Metal Together with a 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.

Hackaday Prize Entry: Welding Plastic Filament

There are a lot of neat toys and accessories that rely on 3D printing filament. The 3Doodler is a 3D printing pen, or pretty much an extruder in a battery-powered portable package. You can make your own filament with a Filastruder, and of course 3D printers themselves use up a lot of filament. [Bodet]’s project for this year’s Hackaday Prize gives those tiny scraps of leftover filament a new life by welding filament together.

The EasyWelder [Bodet] is designing looks a little bit like a tiny hair straightener; it has a temperature control, a power switch, and two tips that grip 1.7 or 3mm diameter filament and weld them together. It works with ABS, PLA, HIPS, Nylon, NinjaFlex, and just about every other filament you can throw at a printer. By welding a few different colors of filament together, you can create objects with different colors or mechanical properties. It’s not as good as dual extrusion, but it does make good use of those tiny bits of filament left on a mostly used spool.

Since the EasyWelder can weld NinjaFlex and other flexible filaments, it’s also possible to weld NinjaFlex to itself. What does that mean? Custom sized O-rings, of course. You can see a video of that below.

The 2015 Hackaday Prize is sponsored by:

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Sodium Pickle Lights

A few weeks ago, the folks at the 23b hackerspace held Sparklecon, an event filled with the usual infosec stuff, locks and lockpicking, and hardware. A con, of course, requires some cool demonstrations. They chose to put a pickle in an arc welder, with impressive results.

This build began several years ago when the father of one of 23B’s members pulled off a neat trick for Halloween. With a cut and stripped extension cord, the two leads were plugged into a pickle and connected to mains power. The sodium in the pickle began to glow with a brilliant orange-yellow light, and everyone was suitably impressed. Fast forward a few years, and 23b found itself with a bunch of useless carbon gouging rods, a 200 Amp welder, a pickle, and a bunch of people wanting to see something cool.

The trick to making a pickle brighter than the sun was to set the arc just right; a quarter of an inch between the electrodes seemed optimal, but even then pickle lighting seems very resilient against failing jigs made from a milk crate, duct tape, and PVC. Video (from the first Sparklecon, at least) below.

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Spot Welder; Don’t Buy It, Build It

Spot welders are super handy for making sheet metal enclosures for your projects. The problem is, commercial ones are rather expensive… The good news is, they’re actually really easy to make! This is [Caio Paulucci’s] first submission to Hack a Day, and it was a weekend project him and his father just finished.

A spot welder works by dissipating large amounts of heat in between two electrodes in the material you are bonding. It makes use of a transformer that converts mains voltage to a very low voltage, but high current energy source. The cool thing with this type of welder is it’s perfectly safe to hold onto the electrodes as the voltage is so low, you won’t get electrocuted. By running a super high current (generally >1000A @ ~1-2V) through a small surface area, you can super heat most materials hot enough to weld them together.

They can be made using the transformer from a microwave, some heavy duty welding wire (generally 2/0 or thicker), and a few other odds and ends such as wood, electrodes, and maybe a few nuts and bolts. At the most basic level, you are basically re-wrapping the transformer’s secondary coils to change the ratio to produce a low voltage, high current transformer.

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Current limiter for a MOT welder


[Mike Worth] wanted the option to run his Microwave Oven Transformer welding rig at less that full power. After being inspired by some of the other MOT hacks we’ve featured he figured there must be a lot of ways to do this. But his searches on the topic didn’t turn up anything. So he just designed and built his own adjustable current limiter for the welder.

At the beginning of his write-up he details what we would call a bootstrap procedure for the welder. Go back and check out his original build post to see that he had been holding the framework for the cores together using clamps. To make the setup more robust he needed to weld them, but this is the only welder he has access to. So he taped some wood shielding over the coils and fired it up.

The current limiter itself is built from a third MOT. Adjustment is made to the cores by changing out the E and I shaped pieces. This allows for current limiting without altering the windings. [Mike] holds it all in place with a couple of bicycle wheel quick connect skewers.

It just goes to show that you should never get rid of a microwave without pulling the transformer. Even if you don’t need a welder wouldn’t you love a high-voltage bug zapper?

DIY spot welder makes metalwork easy

At Hackaday, we’ve seen enclosures built out of just about every material. From wood, glass, epoxy resin, plastic, and even paper, all these different types of enclosures provide some interesting properties. Sometimes, though, you need an enclosure made out of metal and welding together steel cases isn’t exactly easy or cheap. [manekinen] came up with a really great solution to the problem of welding together sheet metal. It’s a very easy to build spot welder perfect for fabbing steel cases.

The core of the build is a transformer pulled from a Technics stereo amplifier. [manekinen] removed the stock secondary winding and rewound the transformer four turns of 35mm ² wire (about 2 AWG). This made the transformer put out 2.6 Volts a 1 kA – more than enough to weld 22 ga sheet.

For the control mechanism, [manekinen] put a limit switch on the electrode arm and wired that to a timer. A knob on the front of the welder allows him to vary the time the welder is on from 0 seconds to 4 seconds.

The results are fantastic – trying to rip apart a weld only results in the metal itself tearing; exactly what you want to see in a welder. It’s a great build made even more fantastic by the welder building its own enclosure.

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Hundred dollar capacitive discharge welder

[Robert] needed to weld metal tabs on a few batteries. In a proper manufacturing situation, this is usually done with outrageously expensive welders. Not wanting to spend thousands of dollars to attach bits of metal together, [Robert] built his own capacitive discharge welder for only $100.

Instead of the giant transformers you’d find in a spot welder, a capacitive discharge welder uses a huge bank of capacitors – greater than 1 Farad – to weld pieces of metal together. Huge caps like these are commonly used for ridiculous car stereo setups, so with the addition of a car battery charger purchased from Walmart, [Robert] had most of a welder on his workbench.

To control the mass of power coming from his huge cap, [Robert] used a 13o amp Silicon controlled rectifier to improve the control of his welder. With the battery charger, cap, and SCR, [Robert] only needed a few bits of heavy gauge wire to tie the entire build together.

[Robert]’s build welds metal tabs on battery terminals beautifully, but the possibilities don’t end there. This welder could easily be repurposed to build the skeleton of outrageously intricate dead bug circuits, or maybe even keeping that thing you made with your Erector set in one piece permanently.