MOT failure, welding advice please!!

[salty_monk]

Hi guys, long time no hear - sorry!

Car failed it's MOT, four bits of welding, & the stop lights (see post in electrical!! )

So... have borrowed an SIP Migmate 105 turbo with gas.

Have welded with oxy acetylene before & mig once (where I worked & it was all setup for me ready to go!!).

What setting should I use? It has: on/off. Min, med, max. High/low. Wire feed speed dial. Is it just a case of try it and see??

Bits to weld are, front of chassis member (the one that goes front to back) then a small hole around 3" away from the front leaf spring mounts on both sides plus a little hole at the rear of the leaf spring in the corner where the side meets the boot.

Presume I will have to thoroughly clean up the area & eradicate any traces of hammerite & under body wax, also know there is cavity wax near here (hence the reason I don't really want to use gas), do I just have someone nearby with a mister spray & a hose for ultimate backup?

Last question... What do I do with the vehicle electrical connections bearing in mind I'm still positive earth & dynamo? Do I need to disconnect the battery &/or dynamo or not? I'm pretty sure I don't but want to check it out.

Thanks a lot, Dan

[Chris Morley]

Try it & see on a bit of scrap steel first or start at the lower settings and work up until you get a nice crackling sound and the wire doesn't judder. The hose is a good idea -chances are that the old wax won't catch fire & it will simply smoulder but don't quote me on that. Remove any carpets, underlay and seat covers near the area to be welded. For the battery, simply undo any of the connections to the battery (either terminal) to prevent a circuit forming. It probably isn't necessary but it only takes you a few seconds.

I have to warn you - the small holes you describe will probably be bigger. Thoroughly prod around the area within three inches of the holes to make sure you're welding onto sound metal. There's nothing worse than tack welding a patch in place only to blast holes in the surrounding metal when you start welding it into place (been there, done that! ).

[wanderinstar]

I did a bodywork Skillcentre course some years ago and I always remember the instructor describing the noise that came from a properly set up MIG, [excuse me ladies] as being like a tight arsed fart. Get it to sound like that and you should be somewhere near.

[chickenjohn]

I did a bodywork Skillcentre course some years ago and I always remember the instructor describing the noise that came from a properly set up MIG, [excuse me ladies] as being like a tight arsed fart. Get it to sound like that and you should be somewhere near.

I prefer to get my MIG welder to sound "like frying bacon" when everything is just right!

cheers

John

[salty_monk]

Yes, remember that frying bacon sound well from the factory I worked in. I guess if the noise is what you listen for it'll soon come back to me pretty quick.

Will fire it up on some scrap before I start & have a play before I attack the car.

Will have a prod round the holes, the MOT man has done a pretty good job of ripping it all out though!!

Cavity wax is about 14 months old, hopefully it won't catch light, I'll try to get a second body on hand to make sure.. most of the work's in the clean up & prep then making the patches in any case.
I have some 2mm steal sheet someone gave me to make the patches, hope it's not too thick or I'll be off hunting down some 1mm!!

[bigginger]

Don't quote me either, but from playing wirh a thickness gauge (one of the round ones with measuring slots in it), most of the tin seems to be 1.2mm. I don't know about saloons/Travs though, this is on Pick ups, and I coluld be wrong...
It seemed daft to me when I first found it out, but the sound is the secret of success - if you're not getting 'that' sound, you're just melting metal on to the surface.

[rayofleamington]

Hi Dan,
One other thing that is VERY important is preparation of the welded area. You have to clean the metal up until it is clean bare steel with no paint, wax or rust. If a microscopic trace of underseal residue is in the area you can forget the idea of a decent weld
An angle grinder will remove most stuff but when it comes to the black underseal it just spreads it around so you need to scrape it away throroughly before getting the grinder out.

For the rear chassis extension (near the rear spring rear mount) a patch is only going to be a temporary repair and it ought to be done using a repair section.
For patching around the rear spring front mounts, a good job is needed as poor patches won't give any strength and the area can become weak (hence my traveller being off the road due to previous owners' poor repairs in this area which I need to remove and start again)

[SR]

dan ,ello mate ,also when youve got nice shiny metal like ray says ,as u start welding it can burn and turn black, rather than grind anymore away i find a rotaty brush on drill cleans it up nice again, try to check other side of panel for telltale signs of penetration,av a look on my weblink at pic of rear floorpan, u can see where ive seam sealed it from underneath ,a silver/grey line of weld, it can help a lot having a good welder with u a first to point u in right direction,good luck mate,steve

[salty_monk]

I'm not too bad on gas & I have used a mig once before (although it was all set up for me) so I'll get some scrap bits together & give it a whirl!! Will keep you posted how I get on!

Ray, realise a patch is a temporary fix, there's a big lump of a repair on one side as it is that I'd have to remove to put in a proper panel & I just don't have the time at the moment. Will get it through the MOT for now & think about it some more when it's warmer

[rayofleamington]

Ray, realise a patch is a temporary fix

no probs, and yes there's a time and a place for temporary repairs ;-)
The problem with front chassis legs anywhere near the eyebolt and the rear chassis extensions near the spring shackle is that the panel was made with internal reinforcing, so by the time there is a hole nearby it usually coincides with the inner strengthening having no strength left.

[bmcecosse]

Watch out for the petrol tank and petrol fumes when welding anywhere near the rear springs !! I find a good auto-dim helmet is a great help with MIG welding - but I still much prefer to use my oxy/acetylene.