Welding Different Thickness Metals

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Hi,I have a question on welding different thickness metals together.  In short I'm fabricating a downpipe for my car.  I'm going to mill a flange to bolt to the turbo from 3/8", or maybe 1/4" steel and weld on a 16 or 18 gauge pipes to it.  Since I'm a newbie, my question is how to best get decent penetration into the base metal?  Any rule of thumb in general?  My thinking was to set the machine to the pipe gauge, otherwise I'm thinking that I'll burn through the material, but I'm not certain how to get a good joint between the two.  This will be done with a Miller 211, running on 115 volts, maybe 230 if I can get the outlets wired up in my garage.As for my experience, I've welded with most major processes, read/have welding textbooks, but just don't have a lot of trigger time.Any input would be appreciated. Thanks,-D
Reply:What you are proposing to do is hard for even experienced pros.Lots of practice, that is my suggestion.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:If you set for the thinner material you will only cold lap on the thicker. You have to set to where it's melting the thicker material and focus your arc on that. When you get a puddle going on the thicker stuff you move the torch over to just nip the thinner tube. If you go too far over you will blow the tube away. It takes some practice.NickESAB CaddyTig 2200iPowermax 45MM140 (Sold)
Reply:Thanks.  I was trying to avoid the coldlap especially since the part will be subject to vibration, stress and heat cycling.  I figured it would be hard, since I've tried it in the past, with very, very limited success.  I was hoping that I missed something besides my lack of experiance.  Looks like I'm going to get some scraps of each and practice for a while.
Reply:Do 2 passes.  Weld a bead around the pipe at the gauge setting. Then turn up your machine and actually weld the joint across the pipe bead and the thicker plate.Tiger Sales:  AHP Distributor    www.tigersalesco.comAHP200x; AHP 160ST; MM350P,  Spoolmatic 30A; Everlast PowerTig 185; Thermal Dynamics 60i plasma.  For Sale:  Cobra Mig 250 w/ Push-pull gun.  Lincoln Wirematic 250
Reply:I'd run a horizontal J motion. Keep the long part of the J on the thicker material, bounce the short part of the J up onto the thinner material.Don’t pay any attention to meI’m just a hobbyist!CarlDynasty 300V350-Pro w/pulseSG Spool gun1937 IdealArc-300PowerArc 200ST3 SA-200sVantage 400
Reply:Originally Posted by soutthpawDo 2 passes.  Weld a bead around the pipe at the gauge setting. Then turn up your machine and actually weld the joint across the pipe bead and the thicker plate.