Tuesday, June 8, 2021

Making a DIY Spot Welder

One of the ways humans manipulate their environment is through the use of tools. However, not everyone can afford all the tools they might need, and so being able to work around that limitation can be extremely important. 

Back in 2012, the YouTube channel The King of Random posted a video on how to make your own spot welder, mostly out of parts scavenged from a microwave oven.


As I didn’t have a spot welder and could pick up a used microwave for under ten dollars, I decided to give it a try. The most time consuming part of the project was probably disassembling the microwave, mostly because I wanted more than just the microwave oven transformer (or MOT) when I stripped the microwave for parts. Once I had the parts I needed, it was time to rewire the MOT, which  went pretty much as explained in this video

Cutting the weld on the MOT, drifting out the transformer coils, replacing the primary coil, adding the heavy gauge wire, then epoxying the MOT back together were all accomplished with little trouble. However, since I don’t have a brother with a warehouse full of scrap, I went to a big box store and bought the 2 gauge wire along with some other components.

The main purpose in modifying the secondary coil on a MOT is to convert the transformer from high voltage/low amperage to low voltage/high amperage. This allows for high current which can be focused on a small point, enabling it to fuse metal together.

The rest of the project was fairly basic wiring and carpentry. I used the power cord from the microwave along with the power cord standoff to supply power to the welder. I already had a light switch and cover in stock, so I used those.

Rear view of the author's spot welder, showing power cord and switch.

As suggested in the video, I used one of the door sensors and some wire scavenged from the microwave as an activation switch on the moving arm of the spot welder. This adds a good safety measure as the welder won’t send power to the tips until I close that contact.

Side view of the author's spot welder. Note the switch on the top arm. 

Unfortunately, the heavy wire I purchased isn’t as flexible as that used in the video, so I can’t separate the top arm to spot weld larger or more awkwardly shaped pieces. Since I wouldn’t be removing the arm, one change I made to the design was adding wooden spacers between the sides of the main housing and the arm so that it’s less likely to twist or deflect when I close the jaws of the spot welder.

The business end of the author's spot welder. 

I could have spent more time and effort giving the spot welder a nicer finish or giving it a snazzy paint job like in the video, but I’m more interested in function than form, and my home-made spot welder works just fine even if it’s not as pretty as some others.

All told, I spent just over $20 on parts and supplies for this project. It could have cost more, but I already had most of the items in inventory or the scrap bin.

In Memorium: Grant Thompson, The King of Random, died on July 29, 2019. May he rest in peace. 

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