Struggling welding sill

[thepurpleblob]

I've had a Cebora 130A mig collecting dust for ages now and I've been practicing on some 0.9mm scrap and can do but welds reasonably well without blowing holes even if they don't look too pretty.

So, finally, I decide to have a go at welding a small patch around the jacking point on my car. I can't do it. I just instantly blow holes on the car. I mean as soon as it arcs it blows a hole. The mig is on its lowest setting.

I cut back to clean metal and buffed it all up to shiny with a flap wheel. The only thing I can think is that I've been too zealous with the flap wheel and I've thinned the metal on the car.

Any thoughts were I might be going wrong?

 

[octo0072000]

car sills rot from the inside out so yes thin metal suggest you have a look at this welding on a car is a lot different to on the bench you need to be able to weld 1mm or less on the bench most car stuff is .8 mm also have look on you tube loads of welding tips and tricks there

http://www.mig-welding.co.uk/thin-metal.htm

 

[thepurpleblob]

Thanks - but it's blowing through on the very first hit. Really instantly. I can't even get a tack. Is there anything I can do about that? The thin metal techniques seem to assume that you can at least get a quick tack in.

 

[grumpygramps-2007]

what angle are you holding the gun at.

 

[Daz1968]

What wire size are you using as the thinner the wire the less current is used, my 200amp kendo mig with 30amps min it welds very thin metal ok, I can even bridge holes without using copper behind if careful, and I don't even put it on minimum settings. I am using 0.6 wire and 5% gas.
Here is my chart on machine and second pic shows settings I am on,

I found on min settings using thin metal technique it never fully penetrated so had to up the volts and wire speed to get a better weld.
I think you probably have more corrosion inside and metal thickness after polishing outside is really thin.

 

[mike 109444]

As you think you may have thinned the metal (quite possible) try cutting back (with a thin disc) about1/2 to 1 inch bigger the hole you have, then look at the edge of the metal you have removed and see if you have full thickness before trying to weld in a patch. If not the cut back some more! Also check the inside of the newly removed piece to see if there is still corrosion if so you are going to blow through. Now you know why a 2 inch patch soon becomes a 6 inch patch!

 

[thepurpleblob]

I'm using 0.6 wire and I'm holding the torch maybe 30 degrees of the vertical.

Yeh - I tried to cut just to the clean side of the obvious rust so I'm thinking a much bigger hole is the way forward.

 

[octo0072000]

are you sure you are minimum settings 1 minimum

yours look like this one

 

[Wozzaaah]

Thanks - but it's blowing through on the very first hit. Really instantly. I can't even get a tack. Is there anything I can do about that? The thin metal techniques seem to assume that you can at least get a quick tack in.

Without a doubt the sill is rotten! If you can't even get so much as a tack on it then it's like tin foil.
You'll need to cut it right back until you get to the original thickness, if you don't then you'll be doing the same repair next year.

 

[thepurpleblob]

Yes - I'm definitely on the minimum setting (and the same wire speed as that picture more or less). I think I just need to cut more out and pay more attention to the quality of the metal. I'll let you know how I get on ;-)

 

[Lawnmowerboy]

The fit up with the patches needs to be absolutely spot on if it's that thin. cut them oversize and grind the edges bit by bit. Arc up on the new metal and build up a bit of weld for the weld heat to sink into and wash the tacks over to the old metal.

 

[thepurpleblob]

I've chopped the hole a bit bigger and, if I'm honest, it all seems a lot more solid now. Off to spend the next two hours making a patch the right shape!

It's amazing how much time this take.

 

[thepurpleblob]

Now - of course - the welder is acting up. The wire keeps sticking in the tip and "birds nesting" (I think that's the expression) in the machine. Aaargh

 

[octo0072000]

if it's bird nesting you have too much pressure on the roller feed
the wire need to be able to feed but slip if the tip fouls so you don't get the birds nests
sounds like you are suffering burn back you need to up the wire speed a little to stop this or maybe hold the torch further away from the metal

 

[thepurpleblob]

Cheers - checked the roller pressure and put a new tip on it, which appears to have cured the burnback. All seems to be well (for now).

There's too much stuff to remember !!

UPDATE:
Hard work welding upside down but I'm now getting there doing what amounts to loads of tacks. No blowing through. The welding quality varies between stuff I'm very pleased with and other work that should grind down ok.

So... looking ok. Thanks for all the help and advice

 

[rikrobson]

I find the Cebora, certainly mine does birds nest the thinner .6 wire. it much prefers .8 wire. that aside, after many sill repairs, if you don'yt cut back to thicker metal then it will blow through. You don't mention what car it is. I've done several mondeos and thier sills are paper thin any way, particularly half way down where there is a crease in the metal. if its blowing through when you are welding across the sill, i.e. vertically, run a bead of weldd down where you will be cutting out the rotten section. do this 20-30 mm further that you expect. then cut down the inside of the bead. this will give you thicker metal to apply the heat to. The therory behind this is there is more metal to dissapate the excess heat. if you are welding to an ege you half the heat sink. Once done clean up the bead with a flap disc.

 

[thepurpleblob]

It's a BMW 840. I think I got away with it. It was rotten around one of the jacking points. As it happens, I cut back another half inch and I was into good, solid metal. BMW seem to make the sills out of something proper luckily.

The only major trouble I then had was making the repair piece fit perfectly. Where it fitted spot on I'm really pleased with the results. Where it didn't it's a bit messy. However, I think it will do the job. It's all out of sight anyway.

Lying on my back wearing a wooly hat in this weather was the worst bit quite honestly.

 

[rikrobson]

You could try a euro torch conversion. The torch that comes with the box is a bit pants

 

[thepurpleblob]

Another project to add to the list

 

[Jim Davey]

Don't waste money on torch conversions, sell the welder and put the 100+£ saved by not doing the torch conversion towards a better set.
Torch conversions on hobby migs are like throwing good money after bad, you still have to cope with a tiny drive motor/roller combination that can't give consistent wire feed speed from new, let alone after its pushed a few hundred meters for rusty wire through a clogged liner.
Just my opinion of course.