get a practice piece of steel and drill some small holes it and set your mig up until you get a nice weld. (don't forget the copper backing)

fiddle with the wire speed and amps until you get it flowing nicely you want a single weld, at 90 degrees to the panel and a quick weld. Its ok to do it in the same spot more than once but let each weld cool before you start the next one

The bulk head must be CLEAN (both Sides) or you will get a bad weld.

Good luck

Im going to get into oxy brazing for filling in tiny dents that are hard to hit out because of no room on the inside and small rust holes, what materials do you have to use to melt into the metal and where do you get them? And how do you have to prepare the metal being filled? Could you just braze straight over the top of the rusty metal as it is in the image at the start of the thread? or would you have to hit it with a sander etc and make it look shiny and silver. Also ive heard of some paste or "butter" you put on and melt it in first.

Thanks

Use oxy + acetylene gases (or oxy + LPG like I do now), the best filler I've found is nickel bronze. It is less fluid than manganese bronze so is less likely to run away on vertical surfaces.
You can either buy plain nickel bronze rod and use `copper & brass' flux, or buy flux coated rods (nickel bronze is the pink ones) from BOC, or your local industrial welding gear shop.

Power wire brush it to get all the paint + loose rust/scale off it first.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

and how does it hold up to flexing with the panel as compared to just stuffing some body filler into a shallow dent? and how do you shape it? with one of those wooden pallets like you see on youtube vids? When "dry", with a file or coarse sandpaper im guessing.

Also, How to prepare for bog for the whole area namely where steel meets the brazing repairs

Brazing is excellent at handling flex and vibration.
Classic English motorbike frames were brazed. Carbide tips are brazed onto steel for lathe tooling and they are subject to extreme vibration.

Yes Brazing is the ducks guts for anything where their is vibration or flexing.

A word of caution though if you are going to braze any panels on your car.... wash the flux off with Deoxidine, or phosphoric acid (I think these are all sold as rust converters these days) as soon as you're done. It doesn't matter what paint you use, it will not stick to flux at all. Wash it off with deoxidine and then do it again. And then Multipurpose thinners and then prepsol.

As for the area with the surface rust and trying to led wipe it, yes you can, however, you'd be wise to wash it down with rust converter first, and you would need to flux and then tin the panel before you start. Unlike bog, you can apply led wiping over panels once rusted, and it will just trap it in there and stop it getting any worse. Ever.

Just as another option (Doc chime in as to it's suitability) but i have in the past used Silcon Bronze Mig welding wire. This is used extensively in the welding of galvanised steel tube for gates and fences.
I have found that it sticks extremely well to surfaces and is much softer to dress down as compared to high tensile steel mig wire. it is also very easy to build up and fill holes. I used it on my last car to fill many holes quickly and easily.

I really rate it.

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"Investing my Super in a Cooper" &
"Re-living my Surfing Past in a Woody"

If you had a diy sandblaster you could blast it then lead wipe it

Doesn't need to be that neat as the firewall blanket covers that area.

Cheers, Ian

Any one thought of making up a stainless steel drip tray to bolt under the mc? Seems silly to repair the same spot because of a known issue.

Silicon bronze is used lots these days in the repair of modern european cars, it's commonly called MIG brazing.
The specialized MIG/MAG welders they use this in now are optimized for it and worth $50K+.
It will work in a standard MIG machine with straight Argon gas, but results vary. You need a welder with some mumbo, it's not great in 120A toy welders. I tried it on sheet metal but get better results with oxy/LPG brazing.

SiBr wire is good for MIG welding gal as you say, however there are now excellent gasless steel MIG wires available designed for that which are cheaper and can be used outdoors in a breeze.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I know one person that has this exact thing done in stainless nice piece of work but also alot of work.

_________________
"Investing my Super in a Cooper" &
"Re-living my Surfing Past in a Woody"

WOW aleast my welder didn't cost that much but it does have ball$
thanks again for your informative answer Doc

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"Investing my Super in a Cooper" &
"Re-living my Surfing Past in a Woody"

can you braze with those butane/propane kits you can get form auto/bunnings shops?
or bbq gas bottles (LPG?)?

what about doing something with the argon gas from my MIG?

do you HAVE to have 2 bottles to braze? (oxy/ac)

Propane, butane or even propylene (sold as MAPP) aren't hot enough on their own to braze with. Propylene will just about silver solder.

The small oxy propane kits are a lot hotter and can be used for brazing, but possibly not on large things that suck the heat out of the weld.

Forget Argon, the whole point of it is that its inert - you can't burn it. Its a shielding gas used to keep the air away while MIG or TIG welding.

Tim

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1951 Morris Commercial J Type Van
1955 BSA C11G
1961 Morris Mini Traveller
1969 Triumph TR6R
1977 Leyland Moke Californian