MIG Questions - 18g'ish -GAP - Tip direction ?

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I have read a lot of articles about welding body panels etc.... no one ever talks about where to point the tip, gap height from panel etc... there is just a bunch of guys doing the welding and not talking about this other than..... watch the heat, move around etc etc.... there is much more to it than that i would think....Ex..... Butt weld.... two 18g pieces.A dime/nickel sized gap ? yes or no gap ?Torch angle.....  straight up and down or 45 ?Point tip into the gap or on one edge ?I have practiced a fair bit..... with mixed results each way....There must be a general standard that will provide good results ?Thanks for the help.
Reply:18 ga is starting to get pretty thin. For a but joint, I wouldn't have a gap if I could avoid it. If a gap, smaller is better. Biggest thing will be what you have in the machine. .023 wire and gas is the way to go. Bigger wire needs more heat and this makes things harder. Also push, don't drag the bead as this helps reduce heat input.On 18 ga you can usually still run short beads, say maybe 1"-2" without too much problem, but heat build up in the material can start to fight against you. You'll need to move around and weld in different places to keep heat down. Some keep a damp rag around to help cool the metal as they go. Option two is to do small "spots". Maybe 1-2 second solid tacks. When I do this I have the heat higher than when doing a bead. Again you jump around to different places, then eventually come back and overlap previous spots until it's a continuous weld.If you can reach the back of the joint, you can use a piece of copper as a backing to help support the puddle if you have a largish gap of blow a hole and need to fill.Keep in mind that as you increase stick out with mig, you get a colder weld. This can be of use if you have a tapped machine. A slightly longer than normal stick out can give you an in between setting say between tap 2 and 3. Crank the welder to 3, then increase the stick out form say your normal 3/8" to say 1/2" and you will get a puddle that is between tap 2 and 3. It's also useful if you have a tight joint that opens up for a short distance, Simply pull back as you reach that area to cool things off and move back in after you pass the gapped area.All of this is a lot different than welding thicker material. 18 ga sort of fall right in the middle of welding like you would do heavier stuff, or doing spots like you would with thinner steel. Your skill level is probably going to be the determining factor in what works best for you.At lot of this stuff is easier to show than explain. There's a lot of finesse required to do thin stuff. Test pieces and practice will help you dial things in..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:Here is a post from Garagejournal, you may have to join to view pictures. It's FREE, http://www.garagejournal.com/forum/s...ad.php?t=53534
Reply:Leave a gap about the thickness of the mig wire.  Using a copper spoon you'll be able to turn up the heat a little and you'll get full penetration since the patch to existing panel being an open root. I keep the gun perpendicular to the panel with as little stickout as possible. Keep your wire speed a little slower and voltage a little higher, you'll get a nice flat tack.  Make small tacks and move around, running longer welds will increase shrinkage. Grind down your welds and get out the hammer and dolly to stretch the areas that were shrunken by the heat from the welds.
Reply:i second the copper welding spoon or even a plate(aluminium also works) you can use it even without a gap having that clamped to the back will absorb alot of heat
Reply:Allstate/ESAB Easygrind wire works well for me. It was formulated for body shop welding. And it burns so smoothly that I can step weld at low amps. My MM200 has the spot/pulse panel with burnback control and I can dial in that on/off mode so that is how I do it.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.