Variations in amps / volts

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I've been working on learning how to tig ( remember those pics of my lap joints ) and I've been fighting with the same problem of the bead taking so long to form ( 5 inch bead taking 3 minutes to make ).  Well the last two days I've been working on T joints and have had a time of it so I got my instructor involved and he had a terrible time of it himself.  After a while he adjusted the heat up from the max of 55 to 65 then to 103 and back down settling at 78 volts.  He concluded that the machine has issues where leaning full on the pedal it runs weaker and letting off some its at full heat then drops out.  The other instructor tried it out at 78 volts and agreed that it was dropping amperage a little.  So is it common for a machine to have that much of a variation in what the display says and the actual level of volts / amps?
Reply:For starters unless your talking about OCV (and even then its really high), you weren't running anything at 55-103 volts.  Now if your talking about amps, that makes a little sense.Ive never seen a pedal that dropped amperage once you went all the way down but I guess anythings possible.  Did you try running scratch start?What are you trying to weld anyways, joint/thickness/material?Have we all gone mad?
Reply:Any possibility the foot peddle is the wrong model or not fully compatible and made to fit by wiring it backwards?
Reply:Sounds like the pedal may be hosed.  You could look into measuring the actual current so you would know.  A clamp on meter is probably the easiest method, or use a shunt.The voltage should not really be a factor in your problem.  Like mentioned above, the open circuit voltage (OCV) will be around 80 volts, and then when the arc is established the voltage is then a function of arc length and gas type.  So if the arc gap is 1/16" and the gas is argon, the voltage will be around 10 volts +/-.  You can measure voltage at the cable connection lugs on the power supply with a simple DC voltmeter.If you have poor conductivity through your  torch power cable, work cable, and/or the connections, the voltage measured at the power supply will be higher than "normal", maybe 20 volts.The TIG power supply is constant current, so it will up its voltage to push the same current through a higher resistance.  But this won't affect the arc or the weld, since the current will still be constant and the voltage across the arc will still be dependant on the gap and the gas.
Reply:Originally Posted by Big65moparI've been working on learning how to tig ( remember those pics of my lap joints ) and I've been fighting with the same problem of the bead taking so long to form ( 5 inch bead taking 3 minutes to make ).  Well the last two days I've been working on T joints and have had a time of it so I got my instructor involved and he had a terrible time of it himself.  After a while he adjusted the heat up from the max of 55 to 65 then to 103 and back down settling at 78 volts.  He concluded that the machine has issues where leaning full on the pedal it runs weaker and letting off some its at full heat then drops out.  The other instructor tried it out at 78 volts and agreed that it was dropping amperage a little.  So is it common for a machine to have that much of a variation in what the display says and the actual level of volts / amps?
Reply:Plate thickness for most of this has been 16 gauge so you can understand my confusion at why it would take so long to get a puddle to form at 55 amps ( sorry about that but after an 19 hour day things get wonky ).  Simple T joint on steel plate at 16 gauge with the scale removed using a dip technique.  Had the same problem with 11 gauge steel as well.I'm going to try another pedal tomorrow when I go in to see if that clears it up but its the right model as there are several other machines in the shop with the same pedal and they are all the same.Yes I am in classesPedal is fully pressed and the only time that I get burn through is at the end all of a sudden while the previous length of the bead has been a struggle to get a bead to form.I'm going to talk with the instructor more tomorrow as well though I have to get something worked out with him since we butted heads over the condition of the welding booths in the morning when our class comes in and we have to clean up the spatter off the table from the night classes ( sorry but I'm there to learn not clean up after other people ).  As for pics I have some up around here somewhere from when I was trying to do lap joints on 16 gauge and having the same difficulty and not knowing what I do now.  I just realized to that I will be using a new machine tomorrow so I will be able to get a better idea then.I work full time plus school and family so if some of what Im putting down seems a little obscure please tell me that I need more detail, Thursday and Friday are my light days and I will usually be able to clear stuff up while most of you are sleeping.
Reply:Thanks to my daughters favorite veggy for inadvertently finding my other related thread with pics.  I believe that the amps were set the same at 55 and I was having the same difficulty in getting a bead to form.http://weldingweb.com/vbb/showthread.php?t=36562&page=2
Reply:You can also disconnect the pedal, set the machine to "panel" with the same amperage setting you where using before, scratch start the arc, and you should have full amperage.
Reply:IDK that's about .060"I think I'd start the machine somewhere between 60 and 80 for a butt joint. Probably more like 80 to 100 for a lap and probably a hundred or a little more for a t.Of course that's just guessing and I might tweak from there.That is with pedal control. I have never welded without a pedal and really have no desire to haha.Lincoln precision TIG 275Millermatic 140 MIG
Reply:Oh and don't be afraid to go too far. Especially right now. Crank that farker up just to get a feel for it. See how far you can push it before you blow through.See how high you can set it and still weld. This will give you better pedal control since any movement has a much greater effect.Have you played with flat plate and no filler?Just play with puddles and puddle control. Make some puddles on a piece of 16 ga at varying heat inputs and then look at the other side to see when you start melting through.Lincoln precision TIG 275Millermatic 140 MIG
Reply:Setting the machine to scratch has an issue where the arc wont extinguish when the pedal is let off of and the only way I can break it is the lift the gun away from the plate but then the puddle isnt getting the shielding gas for a second or two.
Reply:Originally Posted by Big65moparSetting the machine to scratch has an issue where the arc wont extinguish when the pedal is let off of and the only way I can break it is the lift the gun away from the plate but then the puddle isnt getting the shielding gas for a second or two.
Reply:Originally Posted by Big65moparSetting the machine to scratch has an issue where the arc wont extinguish when the pedal is let off of and the only way I can break it is the lift the gun away from the plate but then the puddle isnt getting the shielding gas for a second or two.
Reply:First things first let me be clear that we are taught little about how the machines work so I was unaware that that is how the scratch process fully works.Ok I went in and found that my pedal was missing so I swiped another and sure enough it is a bad pedal.  I was able to lightly press the pedal and get a weak arc and as a pressed further down on the pedal the arc would get stronger.  There is still a variation in the heat of the machine so I have had my amps set 10 degree's higher than what the book says to get a proper bead going but it does appear that it looses its oomph periodically so it is also a machine issue.  The new machines we have are millermattic 220's with spool guns so I wont be using those till the next mod which is advanced mig.One other thing I found that was an issue is the length of the tungsten sticking out past the rim of the cup, playing around with that yesterday yielded some interesting results and solved one other problem just as working with the taper did.
Reply:The readouts generally can fall out of calibration, and a lot of them have a 3-5% error factor.  The machine can be shipped off and recalibrated by a good repair facility.Esab Migmaster 250Lincoln SA 200Lincoln Ranger 8Smith Oxy Fuel setupEverlast PowerPlasma 80Everlast Power iMIG 160Everlast Power iMIG 205 Everlast Power iMIG 140EEverlast PowerARC 300Everlast PowerARC 140STEverlast PowerTIG 255EXT
Reply:Would that be Valdosta or maybe Savannah south Georgia?
Reply:I think your instructors should have picked up on that earlier. Machines do brake, an experienced person should have spotted and corrected that and not have left you floundering.
Reply:Yeah I hate to judge too strongly with as little info as I have but it sounds like a pretty crapass school.Glad you made some progress though. Sucks you lost all that time with bad equipment.Show us some new pics once you get it dialed in a bit more.Lincoln precision TIG 275Millermatic 140 MIG
Reply:As much as I hate to admit it to some degree you guys are right but I will have to say in my instructors defence that he is pulling double duty as the head of the department and has to handle the administrative paper work since the school has not cleared him to have an administrative assistant.  I'll also say that after watching him tig that it isn't his strong suit as he ended up with filler on the tungsten quite a few times.I'm working on butt joint flat on 16guage with a 1/32 gap and a root and cover weave pass with a bend test putting me two topics ahead of where I was at.  I've completed T joint flat vertical up and overhead and had a successful root on the butt joint.
Reply:Passed my first tig bend test today on 16g butt joint on the first try, the weld was stronger than the plate which cracked and creased out past the heat zone of the weld bead.