Looking for TIG help!

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Hello All!I have been welding one thing or another associated mainly with street/strip cars and mild steel for some time now.  I have used a variety of Lincoln and Miller machines for the MIG process and have had plenty of success- no broken or cracked welds yet.    At this point, I would like to do some work on stainless exhaust systems and I have acquired a Miller Diversion 180 for the job.  I had previously worked with an old Lincoln AC/DC stick machine with which I hooked up a TIG torch and did some welding on DCEN for chrome moly tubing.  I figured it wasn't the best tool for the stainless job and have upgraded.  With the new machine I started doing some practice work on some scrap and coupons which seemed to go okay- sometimes.  What I am mostly concerned with is welding the light gauge exhaust tubing to a heavier 3/8" flange.  I am having a hard time getting enough heat in the heavier flange without over-heating the tubing.  When I reduce the heat setting and/or back off the foot pedal, it seems like I am not getting any penetration on the flange where the weld just lays on top.  I guess I could have picked an easier project to start with... There is a lot of good information on this board that I think is going to help me very soon!  Thanks for any and all comments!
Reply:someone correct me if i'm wrong, but isn't "chromoly" usually 4130 stainless?
Reply:preheat the flange wash from flange to thinneridealarc 250/250 ac-dc tigidealarc 250/250 ac-dc tig #2 used for sticklincoln sp100hh125dual arbor grinder polisher30 yrs of hand tools52 pitch blocks 6p-26prake gauge -pitch gaugeG&D prop repair 918-207-6938Hulbert,okla 74441
Reply:Originally Posted by Taidensomeone correct me if i'm wrong, but isn't "chromoly" usually 4130 stainless?
Reply:so 4130 is a type of steel, also referred to as chromoly, but it's technically not 'stainless'?
Reply:There ya go Taiden.  Look at the number system stainless is like 316L and 4130 is just that.  It identifies the component additives in the base metal  ala .0040 and .30% additives to the original mild steel mix.  Prolly a poor explanation but it works for me.  Hope this helps.BobI'm spending my Kids inheritance, I dont like him that much anyway!!!!!!Enuff tools to do the job, enough sense to use em.Anybody got a spare set of kidneys?  Trade?
Reply:Hello melsie68, first off,  consider what prop doctor mentioned about working from the thick flange to the thin tube. Additionally, pay close attention to the angle of your torch relative to the joint, by pointing the tungsten to the tube you will concentrate the heat there more so, by pointing it more toward the heavier flange you will concentrate the heat there. You have to "read" the heat and point the tungsten appropriately based on your assessment of that. Consider using enough stick out on your tungsten so that you can keep it as close to the puddle as possible, this will allow you the best control of the amount of heat input and where it will be applied relative to the two parts that are being joined. An individual can use a lot more stick out in a fillet weld type situation than a flat butt weld. If you are using a small cup size set your gas flow rate so that it is sufficient for coverage but doesn't have so much velocity that it distorts the puddle(you shouldn't see the gas "pushing" the puddle). Use a small enough filler rod so that you don't have to have too large of a weld puddle to readily melt the filler. A lot of the time I will use various GMAW wires for GTAW fillers, just snip off a length that you can straighten and use it like regular GTAW filler rod. You can buy the smaller diameter rods, but they are likely much more expensive than just using the GMAW wire. Good luck and best regards, Allanaevald
Reply:just a mention but really if you weld the full circumference on the inner edge of the flange, you really don't want to weld a full bead on the outside too, it's much less strong that way, usually you will see header manufacturers just use a few tacks on the outer part of the flange for that reason, strongest connection will be full inner bead & then minimal support tacks on the outer point of the flange, this works best when the primary was a tight fit to the flange holes to begin with... just fyi..miller 330a bp TIGmiller dynasty 200DX TIGmillermatic 185 MIGthermal dynamics cutmaster 101 plasma cuttersnap-on YA5550 plasma cutterhypertherm powermax 30 plasma cutterbaileigh CS225 cold sawetc....
Reply:Thank you everyone for all the insight in your replies.  I will be sure to test out some new things before I get to it on the real project!
Reply:I think I got her done rather nicely for my first try on stainless.  Thanks for the help.
Reply:Originally Posted by Taidenso 4130 is a type of steel, also referred to as chromoly, but it's technically not 'stainless'?
Reply:thanks guys, every day I learn a lot on this forum, so thanks for taking the time to break it down for me