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Microwave owen transformer spot welder?

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PekkaNF:
When I had a Morris Marina 1,8 l TC, I was studying how to use MIG. I got the gat cheap because it had an encounter with a deer. I was able to cut out front pilars and part of a roof from othervice crubled similar car. Fair amout of fitting and welding before windshield, bonnet and doors fitted. MIG had a timer and a special nozzel for "spot" welding. Needed a lot of clamps and preparation to imitate spot welding.

I found one small industrial machine 350€, but it was big. Well over 35 KVA, water cooled and all that.

I found out that just a stone throwing distance away from my work is shop/factory that stock anything you need for carbon brushes and motor/transformet winding. I bought a metre of 25 and 35 mm2 copper rope (used for carbon brush manufacture), 10 mm silicon sleve and class fibere backed adhesive tape good util 155C.

Old isulation had taken a little hit from secondry removal. Put some tape over the core.

I was able cram 2 2/3 rounds of copper rope on the MOT. That produces 2,4 VAC unloaded on secondary. I measured less that sec partial secodary shot circuit (tried to make it short, but it buzzed and arched), primary pulled 14A and voltage dropped 230->220 VAC. Looks like this will do.

I wonder if copper grounding electrodes could be used as a welding arms or electrodes.

Pekka

Fergus OMore:
I think that I can go some way to answer your Mig/Mag issues. Basically, all that was needed to create a spot weld was a modified Mig nozzle or shroud which is nothing but a nozzle with two raised lugs and a a the ability to punch a hole in one of the two sheets of body metal. The Mig nozzle was placed touching the intended join and the hole was filled with metal. As the arc was shielded there was no necessity to use a face shield.

It may interest you to know that some 30 years ago Alan Robinson the Lecturer in Motor
Vehicle Restoration at Gateshead College produced a set of notes for student use and this was subsequently made into a book both in English and Swedish.  A revised edited which adds a Mr Livesy to the authorship is still available and is obviously updated. Again, the Welding Institute in Cambridge, UK produced a series of videos for the amateur and I recall the repair of a MGB  in the Mig one being shown to students on the City and Guilds qualification course of which I was a 'manure' student.

Further digressing does suggest a Mig-Welding.co.uk series of information which may help . What must be remembered is that the actual sticking bits of metal together is the easiest learnt whereas the English Wheeling and panel beating are demabnding prior to pulling a vehicle back in correct alignment once major structural damage has been  undertaken

awemawson:
Strictly speaking, if you use a MIG to 'spot weld' you are actually doing a 'plug weld' which is obviously so when you look at them. (Perfectly sound way of joining stuff though)

As I was reading Pekka's post it went though my mind that ordinary MIG copper tips could perfectly well be used as the tips for a proper 'spot welder' ie one that joins by passing an enormous current though the two metals and joins them without added extra metal by way of filler wire.

Fergus OMore:
Andrew is perfectly correct in describing the joining process as a 'plug weld'.  It does get a bit pedantic when a spot welder has to melt its way through normally used galvanised body steel to create a joint and replace the anticorrosive properties of the zinc- which should- if you get it right- create an as new joint- with(( clears throat again) the same ability to be torn on impact rather than the incumbents. Its all in Thatcham, the exact number of spot welds to be replaced.

Regarding the spot welder, mine had the existing copper arms but with home turned inserts  but in order to reach more inaccessible spots, I made up a set of longer arms in copper with copper electrode tips. However, after discussion with the gurus at Gateshead College, it was suggested that the arms could have been made out of steel again with copper tips.

My present plans are inherently simpler and will utilise nothing more complicated that cheap and easily obtainable copper earth rods material which comes in 4 foot lengths which could have supplied the local Nissan factory where we obtained donor reject Nissan Primeras. Air hacksawing and stitching up almost pristine body panels  was a joy rather than a chore. I did, however, design and make welding clamps to hold the compound shapes.

awemawson:
My spot welder, which is a hand held type,  has approximately 1" diam main arms and 1/4" electrodes. I am always amazed how hot the 1" arms get in use. I cannot believe that it is directly the current flowing in the 1" bar that is causing the heat. I suspect it is the resistance of the brass coupling to the body of the machine and the tips themselves whose heat is being conducted by the fat copper bars.

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