Introduction: Very Low Cost Sheet Metal Spot Welder (Portable & Convenient)


This instructable is a how-to guide on transforming a spoilt microwave, a plank of wood, some 3-pin plugs, T-brackets and wiring into a Very Low Cost Sheet Metal Spot Welder that is also Portable & Convenient

Please note that as the label of the transformer in my picture states "DANGER, HIGH VOLTAGE", kindly take the necessary precautions and not electrocute yourself in due course of this instructable

Step 1: Materials

The low cost of this spot welder can be further reduced to nothing if the following items can be salvaged instead of bought, most of the time i settle for a trade off between the two.

1. Very old or spoilt microwave X1
(junkyards are overflowing with these)

2. Plank of scrap wood X min 2m long
(bed frames are nice usable sources of wood)

3. T-brackets X 1pair
(L-brackets are fine too, but i just had T-brackets handy)

4. Screws X A LOT
(you'll never know when you need these little fellas)

5. 1cm diameter cable X min 1m long
(preferably solid core, however if it is multi-stranded, ensure each strand is min 1mm diameter)

6. Misc wood working tools and electrical connectors

7. 3-pin plugs X2 (optional)

8. PC PSU power connector X1 (optional)

9. Length of metal chain or the like X min 15cm (optional)

10. Terminal strip (1cm inner diameter) X 2pieces

Step 2: Stripping the Microwave Transformer

This step describes how to obtain the transformer from the microwave

1. Dismantle the microwave without touching anything on the circuit boards

2. Look for the high voltage capacitor, it should be attached to the transformer and looks like a pistol magazine with 2 wires coming out of 1 end.

3. Proceed to short out the capacitor with a screwdriver, DO NOT LOOK AT IT, cos the spark is very bright.

4. PURELY OPTIONAL (SAFETY): take a fistful of used staple bullets and sprinkle them all over the exposed connections of the circuit board, this should render any dangerous voltages nullified

5. Remove the transformer (as seen in the picture) and leave it aside, you may also want to keep the magnetron as it contains some awfully strong magnets, but is hell to take apart (for another time)

Step 3: Structural Skeleton

This entire structure is made from a single plank of wood and the only modifications made to it, is to cut it down to length, thus all the wood pieces share the same height and breath

Lengthwise you will need
short piece X1 (almost square)
average piece X2 (about 1.5times the length of the transformer)
long piece X2 (length totally dependent on how much 1cm diameter cable is left over from the coiling)

1. As seen from the picture, the 2 average pieces form the base which the transformer screws onto, in between them is the PSU power connector.

2.Attached onto the front are the 2 long pieces connected by the T-brackets (do not tighten the top screws,as it should be a flexible joint for use).

3.At the front end, just shy of the 2 electrodes, on the underside of the bottom long piece, attach on the short piece for added stability and support.

Step 4: Electrodes

Anyone and everyone who has dealt with welding knows that at such extreme temperatures, electrodes get eaten away like no one's business, thus i brain-stormed over it and realized that the ground pin of 3-pin plugs could  be used as electrodes, they are widely available and cost next to nothing, next i devised a way of attaching them to the spot welder such that they could be changed out as easily as a drill bit of a drill. Below is how to build your own electrodes for this welder.

1. Take apart 2 3-pin plugs and retrieve the ground pins (the longest pin)

2. Take apart the 2 terminal strip pieces and reassemble the metal parts

3. Screw a ground pin onto a piece of copper scrap and insert that scrap copper into the terminal strip's metal pin, screw down the metal pin to tighten.

4. Screw the terminal strip's metal pin onto the wooden plank with the free end pointing towards the transformer, as these will be attached to the ends of the 1cm diameter cable

Step 5: Electrical Modifications

For a spot welder to work successfully, the key lies in ensuring that a huge amount of current is transmitted though the weld spot, as that coupled with the inherent resistance in the work material, produces the heat necessary for a weld to be achieved.

However, the secondary winding of a microwave transformer is designed to do the direct opposite, it is designed to greatly increase the voltage of mains electricity at the expense of decreasing the current, thus has to be modified if the spot welder is to work, stated below is how to do so

1. Remove the secondary windings of the microwave transformer (it is the winding which has no connection to the mains, has smaller diameter wire and more windings), to do this i used an angle grinder with a cut-off blade to slice through the entire chunk, however i would advice caution as the primary windings cannot be damaged in any way if the spot welder is to work.

2. Using the 1cm diameter cable, make as many loops as possible through the space where the secondary windings used to be (in my case that's 3), then extend the rest of the cable to the front where the electrodes are and attach them on, after screwing the finished transformer onto the structural skeleton base plate

3. Some of you may notice the PC PSU power connector under the transformer, i salvaged that from a spoilt PSU and added it on for convenience and portability (just imagine a spot welder with a long trailing cable), it connects to the primary coil as seen in the next step

Step 6: Others

Notice how i used the metal chain to secure the middle piece of wood, i added this for structure strength as you will not believe how heavy that microwave transformer is

The Brown and Blue wires that are attached onto the primary coil are connected to the PSU power connector mentioned in the previous step

An improvement that can be made would be to encase the transformer and to add a fan to the encasement, for safety and prolonged usage as it does heat up with use, however i personally prefer the raw steampunk look of the spot welder as it is now

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