oxygen sensor welding help

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Hi guys,I'm new here and a total noobie at welding.  I need your help with this one.I want to weld an oxygen sensor bung to an exhaust pipe.  Oxygen sensor bug thickness is about 1/4" and the exhaust pipe is probably 1/8" ??  Anyways, as for equipment, I have a Hobart 140 mig machine with a mix gas tank (75%argon/25%co2).  I have welded other stuffs a couple times with it before in the last 3 years or so   The weld is not as nice but it put the two parts together and it held fine for the purpose.  But this one, the thickness is different and one is very thin.  I'm worry about burn through etc.  Also, I like to have some nicer weld this time if possible to prevent exhaust leak.What is your recommend setup for the machine as far as gas pressure, wire feed speed and voltage?  Wire size is ER70S-6 .030 solid wire.Thanks for all the help.Last edited by randomwalk101; 04-01-2011 at 10:45 AM.
Reply:The best settings in the world aren't going to help you if you don't have the skill. I would switch to .023 wire and set the machine to weld 1/8", there should be a chart on the machine . Using the smaller wire will allow you to take more time to making the weld rather then be rushed by the bigger wire. Now go get some scrape exhaust pipe of the same size and a few pieces that would resemble the bung you need to weld and have at it.
Reply:Shouldnt have any trouble at all as long as your not trying to fill any gaps. I just did a bunch of exhaust welding last night and the only thing to really watch for is that you get any paint or corrosion off of the weld area before you try to weld it. As for setting up the machine I would suggest you get a scrap piece of exhaust tube of the same diameter and set your machine so it runs a nice smooth bead without burning through.
Reply:Ditto above 1/8" seems thick for exhaust tubing?????V.
Reply:I've only gas welded something like this before, but I expect the trick is the same. Focus most of your weld on the bung, and just let the puddle "touch" the exhaust pipe. The heat from the bung will be enough to melt the pipe. Also you want your heat setting to match the bung. Use plenty of heat and keep moving pretty quickly. If your heat is too low you allow too much heat to soak into the work while you're waiting for the puddle, and that'll lead to burnthrough.