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MG Midget and Sprite Technical - welding techniques

What is the best way of neatly closing off some drilled bolt holes in an otherwise sound panel?

The rear deck for my car has had a bolt-on luggage rack and various other things fitted to it over the years. I have about 14, 5/16" diameter holes that I want to weld over (MIG). But given the size and gentle curvature of the panel I want to minimise any heat distortion.

Is there any special techniques other than just rapid stitching with plenty of cool down breaks?
Guy

guy -- the technique is as you decribed, but i would do it from the inside -- and put a copper coin or similar over the hole from outside - gives a good finish (as the weld doesn't stick to the copper) then finish with primer/filler and paint.
Mick struggling with the wiring

Guy, either buy or make yourself a "welder's spoon" to back up the panel and then do as you mentioned, weld a bit and let it cool, then repeat until the hole is filled. Move around the panel and any induced heat will be spread more evenly to reduce warpage as well. All a welder's spoon consists of is a copper sheet that the weld won't stick to that you can back up the weld area to keep from blowing out the panel and also to make the weld smoother and require less finishing.


B Young

Thanks both of you.
I had a vague idea that there was a preferred method involving backing the holes up with something of that sort! Does the copper also act as a heat sink? I probably have some very thin copper sheet but those "spoons" look as though they are quite thick.

Not so sure about modern "copper" coins. The current UK ones stick to a magnet very readily for copper!

Just thought - I can slit some off-cuts of 22mm copper pipe and flatten that out. Should work well enough!
Guy

I've flattened copper pipe, and then mounted some strong magnets to it.
Trevor Jessie

I have found from previous attempts, that welding close to strong magnets causes all sorts of strange effects! The molten steel "weld pool" tends to set off on its own once it gets hot enough, attracted by the adjacent magnet!

I think what may work is to flatten the coper pipe and then hold it in position backed by a strong magnet centred on the hole. The copper will prevent the weld from sticking, and if aligned right the magnet should encourage the weld to stay in place and fill the hole.
Guy

I didn't notice any strange puddles, but there was a magnet at each end and they were about 1.5 inches from the holes I was filling.
Trevor Jessie

1p & 2p coins used to be cupro-nickel IIRC, but I seem to remember hearing that the latest ones are copper-plated steel, as it is far cheaper!
Dave O'Neill 2

Before 1992 they were bronze - now made of copper plated steel
James Bilsland

Ah yes, it's the "silver" coins that CuNi
Dave O'Neill 2

Well that was an easy job! Very satisfying. 19 holes now obliterated! As I thought, the magnet thing did strange things. The normal "purr" of a properly adjusted MIG turned into a rasping roar and spatter went everywhere! So I abandoned that and just held the copper against the back of the holes - with mole grips - no one said how fast the copper would heat up!!

And it didn't cost me a penny. Or 2p.
Guy

Helps if you turn up the gas as well, that's all!
Allan Reeling

"no one said"...

no Guy you are right

I just looked and not one of the beggars told you that

quite

Bill did mention

"any induced heat"...

It is fun welding up holes innit and actually quite good for torch handling practice too

:-)
Bill 1

Just the info I wanted !

Got some badge holes to fill in on a spare boot lid.

Great timing Guy - thanks.

R.

richard boobier

What caught me by surprise is how very much hotter the copper plate became, than the immediately adjacent steel! Not a bad thing as it clearly is acting as a heat sink as well as backing up the hole that is being welded. The heat sink will reduce the excess heat in the panel and minimise any heat distortion.

That said, the rear deck panel is a bit buckled anyway - not by the heat but by having a boot rack bolted to it. Nothing that a bit of bodge won't deal with though. But first I need to get it welded back onto the rear end of my body shell.

Richard, are you still hosting that Dalek?

Guy
Guy

Guy,

The Dalek is now well behaved and only exterminates pests in the greenhouse - awaiting the 'Doctor' with the Tardis to take to Auz !

R.
richard boobier

Hi, I'm going to install a bulkhead because I'm fitting a fuel tank in the boot. Does the bulkhead have to be steel, or can I rivet in some aluminum panels?
Cheers, Karl
K W Seddon

Ally is fine but any joints or edges have to be sealed, the requirement is the firewall must be flameproof and leakproof.
David Smith

Technically, you should also seal the holes in the B-post side panels where the wiring loom passes through.

I rivetted some ally sheet over them and passed the loom through a grommet.

I don't know how many scrutineers would pick that up. Daniel?
Dave O'Neill 2

All of them I would hope; I mentioned this to Karl in his other thread...
David Smith

This thread was discussed between 30/03/2011 and 01/04/2011

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