aluminum lap joint

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what has changed.  everything has been going fine in training so today i tried something different a lap weld.  1/8 base metal 3/32 rod 3/32 lathinated tungsten 17 cfh argon 120 amps on a syncrowave 200 which the only thing changed from the factory setting is 7.5 on the balance instead of 7.0 seems to work better for me.  i could not get the arc to focus i just seemed to bounce from one base to the other the only thing i can think of as different is i was using magnets to steady my work on my table is there any way that was the problem.  also my ground clamp was on one base piece and not the table is that my problem.  i have a few days to scratch my head over this one but when i get back home i want to dive right back in.timJust some stuff in my shop.
Reply:A lot of people will argue with me on this idea, but you can test the concept and such on your own.  Magnetism can have a huge impact on the arc, some people believe that AC is not vulnerable to the effects of magnetism, I believe they are mistaken.  This idea is called arc blow.  It can look like a sporatic arc, or kind of like the arc is being blown around by wind.http://weldingweb.com/vbb/showthread.php?t=44125 I made a thread about it, plenty of arguments there.  I would remove any sources of magnetism from the areas you would weld by at least a foot.  Clamps are the way to go when holding things together.Miller 330 a/bp water cooledI believe in gun control, I hold my gun with two hands.  If you want to know why, click here.Buy American or bye America.
Reply:Maybe some idea what you had been doing before that worked fine might help.120amps seems a bit low, but probably doable. We usually have the students set the machines at 150 amps for 1/8" alum. Lap welds are the first joints they do. Before that it's all running beads on flat plate. Usually I suggest they punch it to get a puddle going and immediately add filler and wash it onto the vertical piece to tie the two together and then just go if that makes sense. What you are having almost sounds like what happens when they try to slowly bring up the amps to start..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:pinjas thanks for the reply as you could tell from my post i was wondering about that, still learning and all, but that was my only real difference and  i had three positiond in close proximity to my work.  when i get back on it thursday i will clamp only.timJust some stuff in my shop.
Reply:dsw, thanks for the info, i did try ramping up to 140 or so and as i noob usually go wide open straight out the gate, good or bad, i just could not get the arc to focus. first i will remove the magnets in still a no go i will look to see what else i have changed.timJust some stuff in my shop.
Reply:got it figured out, it seems to have been magnetism, i was lazy and did not use clamps.  before you jump down my throat hear me out.  first off it was a butt joint, too many things going on in the background when i was typing.  i had a large magnet positioned directly behind a verticle 1/8 thick form attaching a 1/8 wall 1 1/4 pipe also held in position by some more pipes, did i mention lazy.  now some back ground,  i pay the bills as a pilot for 26 years now and have first hand experience with electrical fields and magnetic fields.  older airplanes rely heavily on ac current and and as any avionics tech will tell you can be a bear to diagnose a malfunction and can come up a new fault just when you thought you had it sorted out.  most newer aircraft now rely on dc which i guess you could consider to be more stable.  that is why in welding, the guys in the know, tell us noobs to start with dc steel, the kind quit neighbor next door, it is easier to work with due to stability and ac alumunum is the frat house on campus, rowdy and boisterous, and at best you negotiate an agreement to dasagree but work together at the same time.  to the pros thanks again for the advise and inspiration.timJust some stuff in my shop.
Reply:Originally Posted by tbaxlgot it figured out, it seems to have been magnetism, i was lazy and did not use clamps.  before you jump down my throat hear me out.  first off it was a butt joint, too many things going on in the background when i was typing.  i had a large magnet positioned directly behind a verticle 1/8 thick form attaching a 1/8 wall 1 1/4 pipe also held in position by some more pipes, did i mention lazy.  now some back ground,  i pay the bills as a pilot for 26 years now and have first hand experience with electrical fields and magnetic fields.  older airplanes rely heavily on ac current and and as any avionics tech will tell you can be a bear to diagnose a malfunction and can come up a new fault just when you thought you had it sorted out.  most newer aircraft now rely on dc which i guess you could consider to be more stable.  that is why in welding, the guys in the know, tell us noobs to start with dc steel, the kind quit neighbor next door, it is easier to work with due to stability and ac alumunum is the frat house on campus, rowdy and boisterous, and at best you negotiate an agreement to dasagree but work together at the same time.  to the pros thanks again for the advise and inspiration.tim