a little TIG help please

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I'm taking welding in school(Conestoga College, Ontario) and I'm having a little trouble with my TIG welding.I'm trying to weld a T-joint fillet on 10ga mild steel and I'm getting big undercut on the top of my weld, all the way across.I'm using a Lincoln machine(sorry, I don't know the model) and using 3/32nd" filler, usually at around 105-115amps.Any clues what might be causing this big undercut?  I found lap and corner joints pretty easy, all the in the flat(for now) position of course.  I tried sticking the tungsten out a little further, and not aiming right at the edge of the one piece, and I think my angle is fine(maybe not?) at 45deg.Thanks for any help you guys might have.Last edited by Angelis; 01-31-2010 at 02:25 PM.Reason: more info
Reply:undercut to me is melting out some parent metal that then does not get filled..could be a little too much heat(are you using footpedal or are you flat out?) or toofast travel.. angle of 45 might be too far , try more direct angle into the metal, say 75..if  arc length is too long, or angle too much, you lose intensity and th epuddle suffers..
Reply:Torch position has a lot to do with it.  Also STICK the filler, don't dab it.  More filler to fill the undercut.David Real world weldin.  When I grow up I want to be a tig weldor.
Reply:I'm using the foot petal, but I'm a bit heavy with it.Yeah I am just kinda dabbing it, I'll try to add a bunch more.And I'll try some different torch angles too.Thanks for the tips, guys.
Reply:Watch your arc length!
Reply:for T joints in GTAW the proper torch position will always be off centered.  Don't aim right for the root of the joint.Instead focus more towards the flat leg and then wash your torch up the vertical leg.  Dip your filler not in the middle of the joint but ~3/4 to the top.  Or sometimes even right at the top, this will prevent you from getting too much heat and undercutting the top leg. Gravity will do its work to wash the metal back down wards.  Also if you get the right sized cup and stick out you can rest it on both legs of the fillet, this helps a lot with positioning.
Reply:their are two ways to fix undercut with tig. less heat or more wire. all of the other things people have suggested can defiantly cause it as well but at the end of the day in my experience one of the causes is always heat or wire.
Reply:Originally Posted by AngelisI'm taking welding in school(Conestoga College, Ontario) and I'm having a little trouble with my TIG welding.I'm trying to weld a T-joint fillet on 10ga mild steel and I'm getting big undercut on the top of my weld, all the way across.I'm using a Lincoln machine(sorry, I don't know the model) and using 3/32nd" filler, usually at around 105-115amps.Any clues what might be causing this big undercut?  I found lap and corner joints pretty easy, all the in the flat(for now) position of course.  I tried sticking the tungsten out a little further, and not aiming right at the edge of the one piece, and I think my angle is fine(maybe not?) at 45deg.Thanks for any help you guys might have.
Reply:Your heat seems fine to me, though every one is different. Just look at my most recent thread in the "projects and pictures," to see what I mean.http://weldingweb.com/vbb/showthread.php?t=38242 The two things that I find that cause undercut most of the time are, 1: weld prep. Make sure the metal is clean. No mill scale. 2: torch angle. But I think the angles some have suggested will cause more undercut if I understand them correctly. When you have undercut on a fillet like that, point your torch more towards the side with undercut. Without seeing your weld I couldn't tell you if you need more wire or not. Would hate to say you need more wire only to cause you to get cold lap.
Reply:It sounds like your arc length may be too long and/or you are moving too slowly.  On relatively thin material like this, I try to heat an area just long enough to for it to become molten and "wetted", add rod, and move.  Adjusting the torch angle changes where the heat goes.But, I'm far from an expert at this.  That's just what I learned last year from my experience with TIG on aluminum.Electronics Engineer (embedded controls)Miller 200DX w/ Coolmate 3Thermal Dynamics 82 plasma cutterGrizzly G0678 8x30 millPM1440BV 14x40 latheHF 6x12 surface grinder