14 replies to this topic

[Bell-nose]

Hi

 

I've got to replace the following panels

 

• 2 front wings
• 1 front panel
• 2 sills
• 1 dash rail
• 1 full scuttle panel
• 2 "Cows Ears" (underneath the scuttle)

 

I want to restore faithfully back to showroom condition by spot welding with a spot welder where the panels were spot welded not through drilling and welding, all are original heritage panels (where manufactuered)

 

Please can anyone advise if they have done spot welding and if they have the timings / settings for spot welding the:

 

• Wings to the inner panel
• Sills to the door seam (my assumption is the sills are 3 panels thick in total which will be the same as the scuttle).
• The front panel to the inner wing.

 

The rest will be seam welded / welded in the traditonal way but any infor on the above would be gratefully received.

 

Many thanks.

 

 

[skoughi]

Take some scrap bits of sheet metal, smallish size approx 50mm square and the same thickness of the panels you'll be welding, then set the welder at a low setting for power and time. Place two bits of scrap metal between then welders prongs and weld together. At first they may not weld together so you may have to increase power and time to get an actual weld. Once you do get them to stick together then take the two bits of metal and bend them back and fore until they come apart. If its welded correctly then you should have a small hole in one of the bits of metal where its torn out the weld, the full weld will be on the other bit of scrap.

[tiger99]

Yes, that is what I would do too. It is not possible to quote amps, or pressure, or time, based on the settings on one welder and expect them to be the same on another, as the calibrations are most likely only approximate and will vary from one type of machine to another.

 

Mush like MIG, where it is no use telling someone that you set your Clarke 150Te to a certain set of numbers, while he is using a Sealey. It has to be done by test, in actual working conditions.

 

The one thing that is easier with the spot welder is that once it is set for one chosen set of arms and two thicknesses of 0.9mm, as it will be for most of the work, the same settings will apply whether you are using it horizontally, vertically or upside down. Not so with MIG or most other welding processes. But be aware that the welding current will drop if longer arms are used, or there is a lot of steel between the arms (lower edge of outer sill to floor, for example), which affects the inductance of the circuit. A really clever, modern and expensive spot welder will compensate for that automatically, most will not.

 

The state of the art in electronics strongly suggests that DC spot welders, which will be insensitive to steel within the circuit, will be coming within the next decade, and affordable for DIY use a decade later. They will be lightweight as they will use a high frequency inverter and synchronous rectifer instead of a big iron-cored transformer. If you are curious, the driving force is the advent of small, low on-resistance MOSFETs, and you can already get one beefy enough to switch a starter motor. (Pointless way of doing it actually, the traditional solenoid will be around for a very long time.) A dozen or so in parallel is getting towards spot welding territory.

[skoughi]

Forgot to mention to keep the spot welds a certain minimum distance apart, I think it may be about 25mm, any closer and the electric current will go through the previous weld resulting in weak welds. I wish I'd sourced out a spot welder when I was replacing panels on my clubman as it would've saved a ton of work.

[Bell-nose]

thanks for the above that helps.

 

I've got the two wings that i took off to get at the scuttle which are actually in good conditon so i thought i might take them back to the bare metal and have a go at those to test things out.

 

are all panels the same thickness? i.e the inner arch ans the wing?

 

Thanks.

[skoughi]

I suppose it depends on where you've bought them from. I would think that heritage or original panels will be thicker than other pattern panels. I suppose the best way to know will be to obtain some sort of gauge to measure each panel until experience will tell what it is by feeling it. Whenever you change the prongs then its worthwhile doing a test on scrap to make sure the welds are good. The amount of hole drilling, grinding and time you'll save will be considerable. I so wished I'd used one on my car! I remember seeing a spot welder once with two prongs that seemed that they would be pressed up against say a box section and the current maybe would've traveled down one prong and back up the other thus creating two welds. Maybe you or tiger can confirm if such a thing exists!

Edited by skoughi, 16 October 2013 - 06:35 AM.

[tiger99]

I think I have seen someone advertising something like that a while back. Snake oil. The two pronged spot welder is a very bad idea because the current does NOT travel vertically through the joint, and will form very poor welds, if any. There is actually no guarantee that ANY current will pass through the back sheet, and you may well just make a couple of pear-shaped hot spots on the front sheet. A tool that worked properly on that principle would need a pair of electrodes on the reverse side, accurately lined up with those on the front, and would be horrendously complex and expensive.

 

If the replacement panels are less than the proper thickness, it is unsafe to use them. The correct, and only, thicknesses of sheet used in the Mini are 0.9mm and 1.2mm, and it is very easy to tell them apart. Some disreputable suppliers have been using 0.8mm, maybe even less. It may not seem much of a reduction, and it isn't as far as tensile strength is concerned, only 0.8/0.9 or 89% of what it should be. But the STIFFNESS is less than half, especially in compression, so you could have box section members buckle under load, and all manner of other structural problems, as well as a huge decrease in accident protection.

 

A cheap vernier caliper is sufficient to check panel thickness. There is local thinning on deeply curved sections where they are pressed, because the metal has to stretch, but around the edges, anything less than say 0.85mm and the panel should be sent back to whatever cowboy operation supplied it.

[midridge2]

Yes that type of spot welder exists,  i was using one in the bodyshops over 40 years ago.
it was a good piece of kit, very good for welding roof skins on.
its spot welds were as strong as the normal type of spot welder. 
 
Some times its best to try some thing to see if it works rather that slam it to pieces with out trying it.
it was a very common tool used in bodyshops. 

A very good tool to use to measure  the thickness of metal is a S.W.G.  (standard wire gauge)
 

Edited by midridge2, 16 October 2013 - 07:03 AM.

[tiger99]

As an essential part of making a good spot weld is a forging process, brought about by pressure between the electrodes (as any good welding book will explain), just how was the forging brought about by that tool, using single-side access only?

 

The results may have seemed to be ok, but I would suggest that in fact they were not. 40 years ago almost the entire body repair industry was turning out disgraceful work that would never pass an MOT today, so it is not surprising that tools like that were being used.

[midridge2]

So what has changed in bodyshops over the last 40 years that makes the work superior now?
Is this based on your experience of working in bodyshops? no, i forgot you worked with dummies.

[R1mini]

As an essential part of making a good spot weld is a forging process, brought about by pressure between the electrodes (as any good welding book will explain), just how was the forging brought about by that tool, using single-side access only?

 

The results may have seemed to be ok, but I would suggest that in fact they were not. 40 years ago almost the entire body repair industry was turning out disgraceful work that would never pass an MOT today, so it is not surprising that tools like that were being used.

 

More cobblers

[skoughi]

I would like to see one in action and test the results. If tool companies made them then they must've worked. There will probably be a technique to using it properly which maybe a lot me users didn't know which would give them a poor reputation I'm thinking. They would've saved a lot of work compared to plug welding that's for sure!

[tiger99]

Well, actually, having used a number of body shops over the years, due to accidents caused mostly by others, I have seen the industry clean up its act most impressively. The cars I had repaired in the 1970s and 1980s were badly bodged, every single one of them, with no proper rust protection, and I don't think they even used etch primer. They looked ok, but not for long, and the welding was usually a few pathetic tacks. I had some rust repairs done, and they ruined two of my Minis in various ways, by badly executed rust repairs (oversills when they assured me that they were going to cut out the old metal) and damaged the third by fitting the front teardrop mounts incorrectly after a crash repair, making the inner wings crack. The whole industry was under investigation at one time, which is what prompted the MOT rules for welded repairs.

 

Changing legislation, and pressure from the insurance companies, the biggest customers of the bodyshops, forced them to improve. I have had several dealings with bodyshops in recent years, and the industry has changed almost beyond recognition. They have proper quality management, for instance, and you do generally get a good quality of repair, with a decent warranty. In fact I will even recommend one, Aylesbury Panelcraft, for accident repairs. I was seriously impressed by their level of professionalism on two occasions. Another of the new style of competent and professional bodyshop is Parrs of Harrow, who I have not used recently, but in the early 1990s did some very good work for me, actually my first good experience of a bodyshop.

 

So, the industry has changed, for the better, but there are still some back street bodgers around.

[midridge2]

So your experience with bodyshops were bad but that does not mean ALL bodyshops were bad.
Speaking as some one who started in the bodyshops in 1969 for 30+ years the way cars are repaired is basically the same now, right from a small dent to jigging a car.
I have NO memory of the motor trade having to clean its act up because of pressure from insurance companies.
I dont see how having a quality repair manager will now mean that a welding repair will pass a MOT now when 40 years ago it should have failed,  back then most cars that wanted a cheap welding job went to a back street garage not a bodyshop.
At the end of the day its still the insurance companies who set the repair times and try to save money by getting bodyshops to lower the repair times and hourly rate.

[skoughi]

Wow! Amazing how quickly a simple question about spotwelding settings can turn into something completely different! Joys of the internet I suppose.