welding old metal

[Mgazb]

I finally got a chance to start my real welding project - sills on an MG Magnette. I have now discovered that welding to old metal seems to be different from welding new.

I put in a flat repair section, but I found that I was getting a very ridged weld. I was using the stitch technique going round the panel to avoid it getting too hot. Is this likely to cause this?

I ran out of gas after that, so could the (lack of) gas pressure have affected it?

I am still using disposable bottles, but really must get round to bigger ones.

 

[English Steve]

Hi Mgazb.
The old metal should be very well cleaned to remove all rust, oil etc, but other than that I would not have thought it much different to new steel. Lack of gas would result in porous welds, rather than tall ones. It sounds to me like you either need a little more power to burn the spots in, or perhaps you are simply keeping the trigger pressed in too long on each spot.
It is a while since I did any thin sheet welding, but I expect someone with more recent experience will jump in soon.

Regards

Steve

 

[Johnny™]

what is the penetration like? can you visually see the other side? old metal should be easier to weld than new steel as long as its well cleaned. something to do with carbon content.

 

[Mgazb]

I can see the other side, but it's a bit gloomy in there. I'm trying to do lap joints as it won't be seen once I've finished so I'm not sure how to judge penetration. I can see the scorch marks on the other side some of the way round.

 

[fingers99]

Could be your gas pressure. If you can feel the other side, you should have a small ridge (which will be the penetration). If you can't, try increasing amps or reducing wire feed a touch.

As above, get the metal as clean as you can (and remove any coating/oil, etc from the new panel) a flapdisk is ideal.

 

[Mgazb]

I cleaned it all down to bare metal with a wire brush on a grinder originally and I sprayed it with weld through primer as I wasn't able to get on to the welding at the time.

Unfortunately I've not been able to have another go and finish it off. I hope it's still clean enough.

 

[Welder Jay]

if u can get access to a sand blaster try that.its worked in the past for me