Spot vs Mig Plug welding
I have been practicing a lot of both spot welding and mig plug welding and am now ready to decide which application to use. I need to weld a new battery apron and new radiator support in my 68 Mustang fastback. No matter what I choose I realize that I will not be able to 100% spot weld due to length of the tongs of the spot welder.
I will say that I have done peel tests on both my spot welding and mig welding and find both are impossible to tear apart.
The question is, if the spot weld is 3/16" diameter and the mig weld is 5/16" do I simply choose mig welding? I can cut a considerable amount of time if I spot weld all areas that I can reach with the spot welder tongs, followed by the mig welder in all areas that the spot welder can't reach.
What should I do?
Both ways are a pain in the ass and time consuming, the only other alternative would be to oxy/acetylene brass weld (which has fallen out of favor in the last 20 years). I think if it were me doing the job I'd go with the spot welder as much as possible and use the mig/plug welds in the areas the tongs won't fit. What about borrowing or renting a regular bodyshop type spot welder that doesn't use tongs but uses two separate handles/electrodes ? One of the reasons I go with the spot welder is it more closely duplicates the factory welds (on a classic mustang fastback that could be important).
Mixing spot and plug welds is very common. Just as you point out, you spot where you can and plug where you can't spot.
Spot welder info
I have tried the hand held "cheap" spotwelders that clamp on the metal and found them to not be very good. So, I now just plug weld with the mig. I do this as a hobby so it isn't so bad, but for production use I would definitely have a professional setup.
Just curious, how do the hand held tongs work? What clamps the metal together during the weld cycle? How does it perform with layers of metal that are different thicknesses like an outer rocker to inner rocker?
I have one of the ones with the hand held electrodes. It works excellent, especially if you're trying to get that factory look when replacing panels. Generally you need to ensure your work is clean. "Three sides clean" is the expression they use where I've read up about it. You ensure your pieces are tight up against one another. They don't necessarily have to be clamped, but if you can clamp them it works best. If there is a gap between the pieces you will end up with either a very deep spot weld or burn through the outer piece altogether. There is a timer and a voltage control on my unit. You hold your electrodes tight in two spots that you want spotted and hold the trigger. It's a matter of practice and trial and error to establish your settings. After doing it a bit I got to where I would set the timer long and release the trigger once I had sufficient heat/weld, essentially operating it manually. You do not pull the electrodes away as soon as it shuts off. Hold them in place for a few moments while it cools.
I use it for lots of things. When I'm putting a patch in where I'm using the backing strip and butt weld I spot my backing strip in then spot the patch to the backing strip then use the mig to fill it all in. Holds the panel in place nicely and helps to control warpage. Plus it's incredibly fast. Where I'm doing a thicker piece like the rocker pinch weld I put the electrodes opposite each other and weld from both sides.
Another thing I like about is is where you have new panels with the quality factory applied black finish ( I've forgotten the name of the finish)). You can actually spot weld right through it. There are other primers intended for use with spot welding that are supposed to wick into the weld area as it heats.
It's a great piece of equipment and best of all I only paid around $100 for it. One of my better deals.
$100 seems to be the magic number for a good used spot welder. The one I have now is a Lenco Spot that I give a hundred dollars for about 7 or 8 years ago (obviously used). The spot welder I had before the Lenco was the same type but made in Windsor, Canada. It was painted a medium blue with an orange front panel. I think it was made by Precision Products and was called the "panel spotter". I gave a hundred dollars for that one back around 1985 and sold it about 5 years ago for $150.00
Could it have been a Porta Spot? The one I have is blue with an orange front and is made in Ont.
Steve, that is most definately the same "aminal". I had a hell of a time finding new tips for mine. Finally found a welding place in Indianna that mail ordered me a set for a reasonable price. The timer quit on mine about 15 years ago so I just timed the weld by how long I held the trigger, worked fine for me for the next 10 years or so.
I would gladly pay that for one of those even for hobby use. One quarter replacement and it paid for itself as far as I'm concerned. I tried one of those clamp up types from grainger once and didn't care for it at all. Wound up taking it back.
I was thinking those machines are high dollar which is why I never bought one.
The difficulty is finding one at that price. I hadn't aggressively looked for one, just happened to spot it one day in a local web newsgroup. Guy was asking $150, wasn't sure I had that much use for it and told him for $100 I could justify it collecting dust more than using it. He was okay with that. Since then I've kind of noticed them in various places, Ebay and the like. You don't see many of them come up and when you do they seem to want $500 or more. You have to be patient and keep your eyes open.
I'd gladly lend mine to you, but I'm in Kamloops BC, the machines inWinnipeg, Manitoba and it looks like you're in Texas.
Off topic, I sure wish more/all members here would display their location in their profile. You never know when another poster is just around the corner from you and you could share expertise and equipment.