upside down arc welding

[jimms]

Hi
I have a Nexus 150 inverter and was trying to attach a plate 4mm thick over a hole on some more 4mm thick, got the top weld an sides done but is there a Knack to the underside weld, I'm using 3.2 6013 rods at approx 100 amps

thanks

 

[Delgado]

Personally (and I'm no 6g expert), I would use 2.5 mm electrodes for what you are doing, as they are easier to control due to the smaller weld pool and lower metal deposit and are far mor suitable for the job that you are doing.I would do the top and overhead weld at "X" current (not sure what the correct current would be as I would use 2.5s, although 100a sounds about right with those rods) and the verticals at a bit less if welding up hill (although with those rods you could do the verticals downhill at 100a). As for technique, do the overhead weld the same as the weld you did at the top, only upside down. By that i mean, move the electrode along the join, pointing it in at 45 degrees to the join and dragging it slightly. I like hold the torch with 2 hands when doing overhead welds, kind of making a "T" shape with my arms, my right elbow would be out to the side at about 45 degrees to my body and my left elbow would be against my chest, with my left palm supporting my right hand(which would only be gripping the torch lightly, so that the muscles in my wrist/arm don't lock up and restrict my movement).

Practise on a few pieces of scrap and you should get the hang of it quite quickly, also, to make sure you get fusion at the start of the weld, after you strike the arc wiggle the electrode slightly from side to side in the weld pool before you start moving forward.

Hope this helps!