Welding body panels - scary stuff.

[yorkshire_spam]

First time I've ever welded anything that thin, putting a patch on the bonnet/wing (http://yorkshire-spitfire.blogspot.co.uk/2013/01/worse-than-wiring-bodywork.html)
Scares the hell out of me doing "delicate" stuff like that, but I guess it could have turned out worse.
One of these days I might get to do something other than wiring and bodywork!
;)

[Sheepy]

Just take your time, don't weld it in one go, or the panel will be all rimply!

Spot weld it all round at different points to keep the heat distortion down, until it's welded fully.

If your still nervous, do a few welds, 4.or 5 then leave it for a minute or two, then go back do some more, then leave it, and so on until it's done, less likely for it to warp.

Grind back the paint so you know you have all the rot out! Good luck.  ;)

[yorkshire_spam]

Thanks Shaun. 1/8th plate and bloody loads of AMPs - I know where I stand. Nasty thin stuff....gah.... sooner or later I'm gonna end up blowing holes in it!

[Anthony]

Buy lots of scrap metal and practice like your life depended on it


And whilst you're practicing, do everything wrong on purpose

IE:  Set the wire speed too low so you can see it burn-back

Set the power too high so you can see it burn holes in the metal

etc,etc.......


You need to learn what is feels like when you're welding incorrectly, and the only way you can do that is by actually doing it incorrectly

Do it wrong, and change one thing at a time so you can see what impact it has

The more mistakes you make the faster you'll learn


You don't want to make mistakes on your car, so make them on the scrap metal

[yorkshire_spam]

Thanks Anthony - I'll get some scraps together and try it!

[JohnD]

If I may add - learn to 'dither'!

This means moving the torch about across the seam, as you make the weld.
Start on the thicker side of the seam, and then move the torch across to the other side, along a slightly curving track, like a letter 'c' with the open side pointing in the direction you are going.  Continue back and forth, advancing along the seam as you go.
The speed with which you do this dithering dance depends on the thickness of the panels.  Spend less time on the thinner one, if there is one.
It's this dither that produces tha lovely wavelike pattern in a professional weld, but it's not just cosmetic, it ensures that the two sides are properly amalgamated into the weld, and minimises the local heating to make blow through less likely.  Ty it with your practice pieces.

See this video for what I mean.  He is welding massive pieces, and uses a looping technique, rather than the c-dither, but that's a minor detail.  Keep the torch moving all the time!
http://www.youtube.com/watch?v=w4RrDeUKcH4
John

[RedRooster]

Buy an active mask, they are not expensive nowadays & make starting the weld so much easier than prodding around in the dark.
RR

[yorkshire_spam]

Wouldn't be without an active mask - wish I'd bought one years ago, couldn't believe how much easier it made things!

[willcolumbine]

When I'm doing thin stuff I always make sure the fit up is really tight - nothing worse than trying to weld air and melting the edges! I've also found it helps to use a backing peice and I've now got a thick piece of copper specially for the purpose. That sucks the excess heat out of the welding area and seems to keep things nice and flat.

When it comes to the welding itself, I usually start by tacking the piece in. When it comes to doing the actual weld, I've found a 'pulse' technique works best. I normally start over one of the tacks and then after a second or so, release the trigger. After a second or so, and with the weld still hot, I then pull the trigger again and roll the next short weld off the previous one. I don't normally do more than a few cm at a time to keep the warpage down.

It's worth looking at your machine too. Minimum amps on most is about 30-35 but some cheap and nasty welders can have double that and that's really going to make thin metal a challenge!