One Tank Stainless

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Ok, my next project is fabricating a stainless exhaust downpipe. I plan on using TIG for the joints. My question is can I use the 100% argon with the mig ( and stainless wire) for tacking these joints ?  I am trying to get by with the single bottle of A instead of buying/renting another bottle. I don't do enough to justify it.Larry
Reply:Sure. Stainless MIG with 100% argon doesn't make the greatest bead, but it'd be fine for tacking. Not sure why you need both MIG and TIG for the job though. .I mark with a sharpie and tack on the back with a TIG, then check fitup. Life is too short to be swapping a bottle back and forth. I made this stianless downpipe for an 850 turbo a few weeks ago:No mig or crazy tacking with the parts installed was required. I would try just marking it and only using TIG.
Reply:You should be fine for "placeholder" tacks.Make them quick though, just enough to hold.  If you don't backpurge and get sugaring/oxides on the back of the tubing, you will run into all sorts of trouble come TIG time.
Reply:Thanks Capnbondo ! That looks exactly like what I'll be tackling after some practice welds. I hadn't though far enough ahead about the marker- that will work much better. Mine is for a Saab 9-3! Hope my welds look as good as yours.
Reply:Originally Posted by lrr81765Thanks Capnbondo ! That looks exactly like what I'll be tackling after some practice welds. I hadn't though far enough ahead about the marker- that will work much better. Mine is for a Saab 9-3! Hope my welds look as good as yours.
Reply:Just make one mark. Tack the part on- use 3 tacks, not where the mark is obviously.Do this one piece at a time- you have to plan ahead a little for it to work though, which takes some practice. I put the first elbow on the flange and knew that the downpipe would be one 90 degrees, then a small piece of bend, a straight, and another 90. So knowing that I knew how to "aim" each piece as I went. If you screw up and need to rotate the pipe, clean the single mark off and re-mark. No need for multiple witness lines. Once the whole thing is tacked together, clean the marks off (since you want to clean the joints in general) for final welding. Hope that  makes sense, how to "plan" it is hard to explain or teach, it's just an excercise in spatial thinking that comes with practice.
Reply:Thanks ! Here is what I am going to try using some mandrel bent tube. Attached Images