Joddled join - why brown marks

[Harry Worth]

I am practising joddled (overlapped) joins. When the weld seems OK ish the surrounding metal is fairly clean. Where the welds are not so OK ish I get a deep surrounding brown stain (that's inviting a comment in its own right). What does this tell me about where I'm going wrong?

On a second note, the work piece has become quite distorted - would it be sensible to use the short pulse method - i.e. a series of tacks or am I working too quickly and should I leave quite a period between each run. Should I try the zig zag thing. I've noticed that spiralling along the joint seems to give a 'neatish' weld - is this an acceptable technique? Still distorts of course but gives a wider weld to bridge a bigger gap.

picture 1 is the top, pic 2 the reverse - the welds don't go quite to the end as I was holding the plates together with a couple of clamps.

Comments please.

 

[Harry Worth]

Seam weld

Thanks - the technique I am trying to sort is for replacing a floor pan - I understand from all that I have read that I have to have a continuous weld to meet MOT requirements. I would like to butt weld but I am realistic in that even if I can get a good weld for this sort of distance I will never be able to accurately cut the floor to fit.

 

[tux]

My understanding is also that you do indeed need to seam weld on a floorpan for the MOT. Plug welds should only really be used wherever panels were spot welded at the factory.

Not sure what the brown staining indicates though I'm afraid, I'm a bit "green" in that area myself.

 

[malcolm]

The brown soot has nothing to do with the type of welder of wire. And here's how to do plug welds with a Clarke on 0.6mm wire. Not as difficult as Captain Broken Record would have you believe.

Many car manufacturers use spot welds. You can use plug welds so long as you keep the seams in the same place as the original panel. Otherwise it's a repair and should be fully seam welded. Car manufacturers rarely lead load - modern seam sealers both side are used.

The soot is vaporised metal that lands on the steel outside the reach of the shielding gas. You'd expect a bit outside the heat affected zone (as in the very top of your photos) but having it beside the weld suggests your torch is as slightly too high an angle or there's not quite enough shielding gas.

Your welds are tall and thin. Probably because you are moving too fast and/or the wire sped is a little high. Second pic is better.

For distortion on a large panel - tack the whole thing with tacks an inch apart. Weld an inch, then move to a different part of the panel weld another inch. Take plenty of coffee breaks and don't let the panel heat up.

 

[Chickenjohn]

Malcolm has said pretty much everything I was going to say! Just a few points to add- use zinc weld thru primer between the two pieces in an overlap (prevents rust). Use a hole punch to make the holes for plug welding- don't do two overlap welds as you did on the practise piece. And if you cant get a clamp on the two pieces, then use self tapping screws or self drilling screws to hold the top and bottom parts of the overlap together tight while you make the plug welds. Then remove the screws and weld up the screw holes as well.

Plug welding technique is ok for welding new floors onto the horizontal lip of the inner sill, but if you are cutting the rust out and welding in new metal to fill the hole, then it is better to butt weld than lap weld, and the weld needs to be continuous.

At the moment, though- do some more practise. Try and get the weld flatter and improve your aim- maybe more light is needed. And have a go at butt welds.

 

[Harry Worth]

Thanks

Thank you for the advice - I have a better lamp but was having trouble with my helmet auto darkening when I use it. Hopefully I can change helmet settings to stop this. Am I correct in welding the seams both top and bottom - I am replacing a complete half floor (if that makes any sense) and have been advised by a pro restorer that this overlap technique is the way to go since it allows for some error and adjustment when welding to the remaining strip of floor.

 

[Richm]

Who is captain broken record? or have I missed something..

 

[Harry Worth]

Captain Broken record

Blink and you miss it - Yes Rich there was a reply to my question which is referred to - the reply appears to have disappeared.

 

[Wozzaaah]

Just to clarify, the reply was deleted by the member who posted it, not one of us site staff.

 

[brightspark]

its called a retracted statement musta been bad advice