DIY Spot Welder Build and Resources

[Preso]

Hello machinists.
I have just recently completed building a small spot welder based on the ubiquitous microwave oven transformer which has been rewound to supply around 2.5V and, I am guessing because my ammeter won't range that high, around 1000 amps. I wanted to end up with a machine that looks professional and functional so I used home made aluminium castings for the mechanical components and a digital timer relay to control the weld time. I saw lots of similar machines on YouTube but nearly all of them, although electrically similar to mine, were constructed using wood and aluminium extrusions or fabricated steel. I know that many home builders must work within the capabilities of their shop but my version was more about the build and less about the need to own a spot welder.

The design for this welder is based on the Aston portable spot welder which was supplied to many secondary schools in Queensland, Australia. I used one of these machines for many years when I was working as an Industrial Technology teacher however since retirement I no longer have access to the machine. Working mainly from memory and from a few low res photos that I found on Google, I was able to replicate the mechanism which is used to lift and clamp the welding tongs.
The Aston welder looked like this:


I made use of a wide range of disciplines to get this build done. They include:

• 3D CAD modelling for designing and verifying the design. I use Autodesk Inventor although I also use Fusion360 if I have to do a lot of CAM.
• 2D CAD for creating the engineering detail drawings for each part.
• 3D printing for creating the patterns from which I cast light alloy parts used in the clamping mechanism and the chassis of the front end.
• Metal Casting for the more complex parts where strength and durability are important.
• CNC machining of some of the slots and pockets in the parts. I also drilled all the cooling holes and a decorative hole pattern in the casing using a generated toolpath.
• General lathe and mill machining for the more straightforward features
• Laser cutting and etching for making the switch panels and for validating the clamp mechanism. I do this by making a 2D mockup from acrylic sheet so that I don't waste a lot of time on metal parts only to find out that the mechanism doesn't work as I expect it to.
• Powder coating for finishing the metal components.
• Electrical and electronic control systems for the weld timer, cooling fan and the heavy current switching.

I am posting this here because I spent a lot of time producing three YouTube videos (with two more in the pipeline) and to date none have rated much in terms of views. I wanted others to see how it could be done as a truly engineered design but if I were a "Diresta" or a "Stefan Gotteswinter" I would have had thousands of views by now but as a relative newcomer I guess that is not going to happen.
If you would like to see more details about this build you can find all the engineering data over at Thingiverse DIY Spot Welder (Super Scary Weldy Thingy) by Preso - Thingiverse
The videos are on YouTube. I will post the url's here so you don't get distracted by all the funny cat videos.
Super Scary Weldy Thingy Part 1 - YouTube
Super Scary Weldy Thingy Part 2 (DIY Spot Welder) - YouTube
Super Scary Weldy Thingy Part 3 (DIY Spot Welder and how to make it go) - YouTube
Please feel free to comment on the videos and the Thingiverse post. Use any or all of the information if you wish. I'm all into sharing and we shouldn't spend all our time reinventing that round thing they put on cars.
Regards,
Preso

 

[SAG 180]

Looks really good, and probably runs better than a commercial unit. I would love to see a home-made spot welder powered by a 2 tonne flywheel, homopolar generator, you could do some serious spot welds with a hundred megajoules or so.

 

[JST]

Seems like even the welders from the US place with "harbor" in its name can do better than that 1000 A.

At least I know at one place I had to use one and got it to do good consistent welds in 0.020" aluminum, which takes a good bit of heat. It was over my largest meter range, which was 1500A. It takes less current to do steel, 1000A may do that in thinner gauges.

Interesting project, I guess, but not a viable commercial enterprise.

Didn't quite mean to be that negative..... the execution is good. it LOOKS commercial. But we are not 'about" hobby type tool builds here. try this:

http://bbs.homeshopmachinist.net/forum.php

 

[eKretz]

Looks really nice, good quality work. Don't mind the naysayers.

 

[EPAIII]

He didn't say it was 1000 A, he said he couldn't measure it due to limitations of his available meter(s). If he is getting good welds, then it is a good welder.

Microwave transformer: 115V input, 2.5V output = 46 in/out ratio. So if it is drawing 20 Amps, then 20 x 46 = 920 Amps. Perhaps it is even less than 1000 Amps.

Good project.

 

[SAG 180]

He didn't say it was 1000 A, he said he couldn't measure it due to limitations of his available meter(s). If he is getting good welds, then it is a good welder.

Microwave transformer: 115V input, 2.5V output = 46 in/out ratio. So if it is drawing 20 Amps, then 20 x 46 = 920 Amps. Perhaps it is even less than 1000 Amps.

Good project.

He's in Australia so the mains is 240V, it would be close to 100:1 winding ratio. Those microwave oven E-I lamination transformers have a core area that would get you about 1000W if you are lucky. you could get two microwave transformers and stack the cores side by side to get a more powerful but elongated transformer but then you have to wind a new primary. Probably easier to get two identical MOTs and parallel up two identical high current secondaries.

 

[rcoope]

Great project Preso, the finish is excellent for a "home" build and you picked the right tool to make yourself. In my reasonably recent experience it's actually quite hard to get a good new 15 or 25KVa spot welder, though I guess the miller spot welder is good and perhaps similar in power to what you have. Anyway, can you give some idea how thick CRMS or stainless sheet you can weld? We have a 15kVa import spot welder whose limit for reliable welding is about two pieces of 16Ga CRMS, better if you clean it.

 

[Preso]

Thanks to those who are giving some positive feedback. I must admit that I have not done a lot of real world testing with this welder. At the time I began the project I had planned to refurbish some 2.0Ah lithium battery packs for my Milwaukee cordless drill. This meant that I would have to spot weld the conductor strips onto the ends of the new cells. After doing some research I realised it was hardly viable to repack the batteries so I just purchased new genuine batteries. However by this time I was more or less committed to the spot welder project. I took the view that it would be nice to have such machine for future projects. I have welded some 18g stainless steel with it but the weld nuggets are quite small, around 1mm diameter but of course you can put as many as you like along the seam. It was never meant to be a viable commercial enterprise. It was meant to be a hobby type build. Maybe I misjudged my audience by putting it on this forum.
Regards,
Preso

 

[DDoug]

Don't mind the naysayers.

It was never meant to be a viable commercial enterprise. It was meant to be a hobby type build. Maybe I misjudged my audience by putting it on this forum.

Yes, if you'd taken time to read the rules, you'd seen that "home shop" is not
for here.

We are not being mean, just advising that there is a better place,
more suited for your postings.

The members who have been here since "Day one" in spite of what our "since date" says.....

 

[eKretz]

Discussion of home/hobby-shop-level MACHINERY is verboten. Posting some of your good quality shop-made tools has always been A-OK. See the thread on the first page that's 8 pages long.

*Another who has been here just as long as you have. *

 

[Preso]

Unfortunately I did not read the forum rules and I can see why some members have made me aware that posts regarding shop made tools are unwelcome. I did check out the Home Shop Machinists forum and I think that is more likely to suit my needs going forward. In my defence I was just trying to make some resources available to others, for free, no strings attached. I am wondering if there are any members of this forum who do make their own tools and might benefit from seeing how someone else might do it regardless of the quality? I have tried to delete this post and to unsubscribe from this forum but so far I cannot work out how to do it. Perhaps some helpful moderator might do it for me.
Regards,
Preso

 

[adama]

LOL don't mind the nay sayers too much.

I oftern have work that a spot welder would be good for, equally i oftern have studs and nuts and such a capacitor discharge type set-up would rock for. I have long toyed with making one with a set of spot weld type jaw arrangement as a discharge path way, problem is last time i played with a big capacitor bank i could not hear for 2 days and no ones electronics in 50' ever worked again!

As others have said, its the magnetic flux limitations of the microwave transformer core that really limit you. Would be far better off rewinding a low turn secondary on a old welding transformer core, some thing with enough iron in it. Problem becomes at much over 1K amps you soon start to need some serious cross sectional area and short as possible leads if your not going to lose most of your power there.

 

[dkmc]

You did a nice job, I just went to HF and bought one
with the 20% coupon......done.
Not an option for you I guess.

If you want views on Youtube, you have to figure out
how to set things on fire, or blow shit up with your
newly completed spot welder.

 

[adama]

^ Whilst its being used by some one sexy too!!!!

 

[SAG 180]

I'd be inclined to stick around on this forum too Preso. There are a lot of forum members running out of a garage workshop, myself included who make stuff for sale or for other manufacturers. Unfortunately you made your post not long after a certain YouTuber began spamming the forum with his amateurish "Look at Me!" type posts where he didn't follow up any of his posts. There were just a string of badly made posts to Youtube about badly conceived projects. I have a few vids on Youtube myself so I can appreciate what goes into making a good one after editing my own into the "barely average" class.

I have built a capacitor discharge spot welder but the high current switching was an issue and really needs some array of cheap mosfets to handle the current. The 1000 Amp SCR blew when I tried to weld two ten cent pieces together. Seriously though, a homopolar generator would allow storage of mechanical energy in a conductive fly wheel (copper or bronze disc) in a magnetic field which would then be dumped in an instant into the spot weld joint. Like the capacitor discharge welder it doesn't place a huge drain on the mains and could even spin up the flywheel with a petrol motor to be truly portable.