Tig welding mild steel tubing

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I am finishing a header I had recently made. The tubing is 18ga mild steel and I butt all of the joints. My joints are very tight for the most part. They are tacked in four places at each joint. I have some experience Tig welding rollbar tubing but never anything thin like this. I was thinking of using a .040" 2% thoriated tungsten and a thin filler rod also about .040". My intent was to hopefully get the filler rod melting slightly faster than the base metal so that I don't burn through. Can anyone guide me in the right direction if I am going with the wrong approach. My machine is a Lincoln PT 185 if that matters. BTW, My machine has a basic pulser. I would assume the faster the pulse, the less heat? or chance of burn through?Thanks for any helpJustin
Reply:I wouldn't pulse it.  It's very tough to use a pulser consistantly going around a complex bundle of tubes.  Its not so much the faster the pulse the less heat.  It depends on how quickly you travel and the amount of time the pulse stays at its peak amperage, among others.You'll be fine with the .040 wire and tungsten.  I do almost a fusion weld, adding just enough filler to carry across the pool to keep it flat or slightly convex.  The other method I'll use if needed is to pulse manually with my foot.  Establish your arc, carry the arc slightly up onto the filler metal, stab the pedal, let off partially when it wets out, and continue on.
Reply:Excellent, thank you for the info.....
Reply:The online converter shows 18 gauge steel at 0.0478", pretty thin alright.http://www.onlineconversion.com/gauge_sheet_metal.htmWith a machine weld, and a handful of practice joints, I could setup a pulse to do this with no filler, but I'd need alot of practice to do it by hand.  Obviously, this will be a challenging weld by hand, since it's very difficult to hold a constant travel speed, arc gap, and torch angle while going around a tube.So, adding filler will probably be necessary to help compensate for the inaccuracy of manual welding, and it does sound reasonable to try either 0.035 or 0.045" wire, similar to the gauge thickness.The 0.040" tungsten will handle up to about 80 amps, and you will probably only be using around 45 amps, so it should be fine, but a 1/16" ground sharp would also be ok."My intent was to hopefully get the filler rod melting slightly faster than the base metal so that I don't burn through."   Not sure what you are thinking here, typically you'll have a full penetration molten weld pool and you'll be dipping the filler into the pool, causing some cooling of the pool and building up to compensate for drop-through and to fill the external concavity."I would assume the faster the pulse, the less heat? or chance of burn through?"  Not really the case, if you want less heat, reduce the current.  In fact the way I look at it, the high frequency is very similar to regular constant current, since the current changes from peak to background (high to low) so fast the arc is essentially a constant average of the two.  If you slow the frequency way down, like 0.5 pulse per second, you will melt a spot weld on the peak pulse, and then chill the puddle on your background pulse, essentially making overlapping spot welds as you travel.Your PT185 only allows you to adjust the peak current and pulse frequency.  The time at peak current and time at background is preset to be equal times (50% Tpk, 50% Tbk), and the level of background current is preset at 50% of the peak.  If you could adjust these settings you may shorten the peak time to 30% to melt the spot in a short time, and give the other 70% for a longer cooling time.  You may also reduce the background current to a bare minimum, enough to keep a stable arc while the pool cools, not high enough to do much melting.Rule of thumb, you'll need about 1 amp average current per 0.001" of thickness, although a slow pulse parameter will generally use less average current than a constant current weld.So say you try a pulse average of 45 amps for example, the peak current setting would be 60 and the background current would be 30 (50% of 60).  45 = (50% x 60) = (50% x 30).  And if you pulse at a frequency of 0.5 pulse per second, you'll get a peak of 60 amps for 1 second, and a background of 30 amps for 1 second, a nice slow cadence that you that may allow you to time the dipping of filler with the peak pulse.  This example may be too hot for your tube, you'll have to experiment.Check out this pulse calculator.  http://www.pro-fusiononline.com/welding/pulseparams.aspYou mention your joints are very tight for the most part.  To make the weld without filler, the joint edges should be square and absolutely no joint gap.  Any reduced material due rounded/chamfered edges or gaps will likely burn through or leave a concave weld.Last edited by pulser; 12-04-2007 at 04:04 PM.
Reply:What they said..And use a Gas Lenz!It will help greatly with the gas coverage..You need all you can get with thin stuff.....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Originally Posted by zapsterWhat they said..And use a Gas Lenz!It will help greatly with the gas coverage..You need all you can get with thin stuff.....zap!
Reply:Ok here is were everbody thinks im a quack. I have welded literaly hundreds of these joints. We purged the inside this is key. We use a 1/16" electrode and we also pulsed it fairly slowly. I do not now the rate but about the same as my Maxstar on its slowes seting. Here is the kicker 90 amp with as little filler as posible. We used this proces for mild steel and stainless 3A milk tubing. Try not to vary the power set it at 90 and and as soon as you get a puddle move and when you stop overlap about a half inch to prevent cracking. Trust me this works great you just need a little practice. Steel Thunder Welding LLC. St. Thomas VI USAMM350PBOBCAT 3MAXSTAR 150 STH375 EXTREME PLASMA6.5 HP COMPRESORDEWALT 18, 24, AND 36 VOLTO/A TORCH SETAND SO MUCH MORE I DONT REMEMBERALL IN MY 2005 2500HD EXTENDED CAB L/B
Reply:If it works for you, you are not a quack.  But we need more detailed info about your process to convert it to use with our various different pulsed TIG machines.  The pulsing terminologly varies between machines, but tell me what your machine is, and what the settings are, and maybe we can make some sense of it.So, you say 90 amps and a slow pulse rate.  I assume that is 90 amps at the peak pulse.  Slow pulse frequency, what is that, 1 pulse per second?What is the background current setting, or the percent of the peak?What is the "% on time", or % peak time, the amount of time that is peak current (90 amps)?