Good Welding Tip Learned Today
 

I consider myself to be a reasonable mig welder but have since discovered that when welding the chassis my welding goes pear shaped. Im used to the 300 amp industrial welders at work which i find very easy to use and i can get really nice consistent welds with. My home welder is an oxford 160 amp mig welder with co2. I can get nice consistent welds with it on sample pieces but as soon as i start welding the chassis i get the odd nice weld and loads of rubbish ones. I thought maybe because you have to work at funny angles and in funny positions so carried on trying, grinding out and starting again where necessary. Talking to our welder at work he said how far away is your earth from where your welding. i normally connected it to wherever was closest to me at the time and welded anywhere on the chassis. This meant that sometimes the earth clamp was one end of the chassis while i was welding the other end.
Anyway I have just been out and tested this theory and it works, I have just done a load of welding with no bad welds! I kept the earth clamp within about a foot of the weld.
So if your getting dodgy welds give it a try.

I've found getting a good earth key, I ended up replacing the cheapy earth clamp and wire on mine to a new more substantial item.

I also noticed some laser cut plates seemed to give a lot more variable weld quality than the box sections, wondered if it was cut from a higher carbon content metal or something.

It depends what material has been laser cut as to what the weld does. Hot roll (HRC) also known as 'black' box section and sheet comes with a layer of black scale,this should be removed before welding to give a better arc. Cold formed/rolled steel sheet tends to be either a light grey colour or bright and is much nicer to work with. It's cleaner and welding arcs seem to prefer it. As for heavier laser cut parts like 5mm+ I tend to clean the edges up back to clean steel in case the cutting has tempered the edge of the material.

first thing you learn when you go to college to be taught to weld. get your earth clamp as close to the weld point as you can.