Tig lap joint on exhaust

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Hello,I am practicing welding exhaust tubing, 16 ga. I am okay when welding butt joints, i get good penetration, though they could look better. However, I am completely struggling on the lap joint where one tube slides in the other. When i go and start the puddle, it takes a long time for it to form and it either forms on the bottom tube, or melts the top edge away. Where should my puddle be formed at? Does it take more power to do a lap joint then butt? Is 1/16th rod too big.On the exhaust the butt welds will be smoothed over, but they wont be on the lap welds so i want them to look nice. Machine: Thermal Arc 150gts, 1/16 electrode and 1/16" rod, 60 amps.Thanks, Luke
Reply:You could use the "lay rod" technique. Lay the rod in the nook and arc on the rod. This should help from burning back the upper material.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:1/16" rod is basically the same size as 16 ga tube, so while it will work, a smaller wire might be a better choice for someone with limited skills. If a student was trying to use 1/16" filler, I'd probably suggest the lay wire method as well. Me I'd probably opt for .035 or 045 mig wire if given a choice.Lap joints are typically easier to do than but joints. But joints are the very last we have students work on, and lap joints are the  very 1st ones. Usually I suggest student start the puddle on the lower plate and wash the puddle up against the edge of the upper one with just a slight bit of torch movement. They should be moving back down to the lower piece when they see the puddle melt away the very edge of the upper piece. You have some what of a challenge to work with for someone new. 16ga is on the thin side for someone who's learning and round tube will complicate keeping the torch angle correct as you move around the joint. Get the arc length wrong or get the torch pointed to much at the slip on piece and the thin edge will melt very fast. You won't have a lot of room for errors here. Couple this with filler that's a bit on the large side and I can see why you are having issues..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:so i can use mig wire? i have some .035 wire and .030 i believe. i thought my rod seemed alittle big but mig wire is not straight. Do they make .035 or .045 in straight pieces for tig? that might be a stupid question.Last edited by luke2; 05-13-2012 at 10:08 PM.
Reply:Luke2 - forget 1/16"I have been practicing on 16 gauge stainless tubing as well and 1/16" will NOT do what you want, ever.  Think your butt joints are good now?  Try thinner filler!  Seriously, the issue is this - you have a base material as thick or slightly thicker than your filler - that means by time your puddle/arc is hot enough to dip filler, the base is already falling in.  You either end up moving crazy fast or pulling back the heat and going too slow.  Arc-zone.com has 0.035 and 0.045 30xL filler wire - MIG wire may work but it's curled.  It's worth it (honestly) to pick up the filler rod since it's straight and nice and rigid.  It made all the difference in my welding so far.  1/16" was freezing  the puddle as I'd go along.Miller Diversion 180Hobart Handler 140 (Soon to be replaced with Miller 211?)Miller Spectrum 625 Extreme
Reply:you can straighten the mig wire..cut a few pieces, chuck  end into a vise, twist  with some tension and it will straighten out to where it will work like a rod..
Reply:hello everyone. I spent some time doing lap welds on 16 ga today since i struggled alot the other day. I attached 2 pictures today of one off the welds. I know they are not good but its my 2nd day.16 ga. mild steel, 60 amps, .045 filler rod, 1/16 electrode.Two questions:-How should the weld lay in between the two pieces. Should it flow from the top piece to the bottom a 45 degree angle, or be convex?-There are little spots on my weld, what causes those?-How can you tell if you got good penetration on a lap weld? What should the back be?Thank you. Attached Images
Reply:That looks good to me.45 degrees is what would want to see. Keep practicing. Half the applicants I see can't do that well.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:Originally Posted by Jon KI have been practicing on 16 gauge stainless tubing as well and 1/16" will NOT do what you want, ever.
Reply:I realize it's sometimes hard to read pictures, but those welds look excessively oxidized to me, not as if from  just a slight film formed while cooling after the puddle has moved on, i.e. post weld. The base metal doesn't look that clean either, although again, I'm judging the picture. If either of those are true, perhaps your gas flow is too low or high or you have a leak somewhere in the system.Dirty base metal is one good way to have trouble with junk in your puddle.
Reply:Originally Posted by Oldiron2I realize it's sometimes hard to read pictures, but those welds look excessively oxidized to me, not as if from  just a slight film formed while cooling after the puddle has moved on, i.e. post weld. The base metal doesn't look that clean either, although again, I'm judging the picture. If either of those are true, perhaps your gas flow is too low or high or you have a leak somewhere in the system.Dirty base metal is one good way to have trouble with junk in your puddle.
Reply:here is the back side of weld. What should it look like...mine is kind of different in spots. some it has the weld coming through, in others it doesnt. Just want to make sure i get full penetration. Attached Images
Reply:70s6 mig wire works good for tig and will actually wet out better than 70s2   I use it all the time on small tube welds for exhaust systems on bikes....On exhaust  tubing 100 %  pen isn't really an issue, your more concerned with just sealing the weld joint and not over cooking the metal.Last edited by B_C; 05-15-2012 at 10:01 PM.  Miller Dynasty 350Twenty Six HammersThree Crow BarsBig Rock
Reply:If your fitup is tight try not using rod (except maybe to start the weld). The top piece becomes the "filler" as it melts back a little bit, like shown below. This is 16ga aluminized 3" exhaust tube.Last edited by MikeGyver; 05-16-2012 at 06:13 AM.Welding/Fab Pics: www.UtahWeld.com
Reply:Originally Posted by MikeGyverIf your fitup is tight try not using rod (except maybe to start the weld). The top piece becomes the "filler" as it melts back a little bit, like shown below. This is 16ga aluminized 3" exhaust tube.
Reply:It's probably possible to measure or estimate the cross section of his weld and the effective circumference of the entire joint and using the strength of the metal, thereby determine the joint strength, but it really wouldn't matter. That joint has reasonably well-fitting tubes and the weld goes around the whole, wide tube. Vibration is only important if it has accompanying movement in the joint which allows fatigue to develop in the weld or HAZ, and because this joint is fully restrained, that shouldn't happen here. In a bad wreck, it might be able to come apart but that's an entirely different situation we don't want to consider here.
Reply:Keep in mind filler does other things for you in a weld besides just add metal. There are usually deoxidisers and other additives that help remove contaminates and alter the chemical composition of the bead. Just blindly doing welds with no filler  isn't the best idea. Like most things in welding, running beads with no filler is a tool. Some times it's the right tool, and some times it's not. Some materials like stainless do well with no filler if your fitup is good. Other times like alum, it's really almost always the wrong way to do the weld. Steel sort of falls in the middle. I'd say in general if you don't know for sure, you are probably best off using filler most of the time on steel..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:thanks everyone for answering my questions. I still have another one lol in the picture below, how do they create a lap weld with no bumps? its almost perfectly smooth. is this done by hand or maybe a robot? Attached Images
Reply:Grind it smooth and polish.In a good SS weld, there is not usually a lot of inconsistency in the surface of the bead, making it easy to smooth.
Reply:Originally Posted by luke2thanks everyone for answering my questions. I still have another one lol in the picture below, how do they create a lap weld with no bumps? its almost perfectly smooth. is this done by hand or maybe a robot?
Reply:that seems like alot of work. The lap welds i have are 1 5/8" slid into a 1 3/4" pipe, so the weld is only 1/16 of an inch. anyone have done this before? i know if i use i grinder i will take way too much off.
Reply:I suggest using a fiat file, emery cloth and a die grinder with a flapper wheel to shape your weld around the exhaust pipe. I also say use filler because it will control the heat input/ cool the weld puddle and the shape of weld bead.Nothing Ever Got Done By Quitting, Never Give Up.
Reply:Originally Posted by DSWKeep in mind filler does other things for you in a weld besides just add metal. There are usually deoxidisers and other additives that help remove contaminates and alter the chemical composition of the bead. Just blindly doing welds with no filler  isn't the best idea. Like most things in welding, running beads with no filler is a tool. Some times it's the right tool, and some times it's not. Some materials like stainless do well with no filler if your fitup is good. Other times like alum, it's really almost always the wrong way to do the weld. Steel sort of falls in the middle. I'd say in general if you don't know for sure, you are probably best off using filler most of the time on steel.