you know, sheet metal doesn't weld all that great with TIG. That said, if you must do it with TIG, I would suggest doing it downhill, but MIG would generally work better.
You will probably find better sucess if the patch is significant is size to weld it in the flat position. Not necessarily due to any travel direction with the electrode or filler metal as it works well in both directions, but rather the problem that is generated by the heat of your tig torch. To draw a loose comparason, think of your tig torch like you would an oxy-acetylene torch. When you weld on the panel with it vertical the excess heat from the flame travels up the panel and adds a tendency to warp the panel. As you weld around your patch, you effectively lock this warp in as the filler metal cools at the edges of the patch panel. The heat warped panel has differing geometry at the edges of the patch panel than does a panel lacking heat warpage. If you begin to watch this closely you will quicly see what I mean. As a young man, I was taught the trade of coach work. This the craft of building bodies and repairing bodies for all sorts of vintage auto and such. Real quickly I figured out that if I could weld whatever paches or new panel segments as were required in a position such as flat, I would have a lot less metal finish work to do after the excess heat generated did not travel up the side of the panel I was building or mending as much. Less metal heated ment less warpage. When you figure that most auto panels have some sort of crown or shape to them, you can readily note that this shape when turned into a vertical plane will effectively "catch" some of the "excess" heat generated in the welding process. Not sure about this? A simple test using only dykem painted around the close perimeter of the patch panel not in the actual weld joint will prove this. Weld one patch panel with described dykem around perimeter in the vertical position as it would be on the vehicle with the wheels on the ground as carefully described in this topic by others. Following that weld another like size patch panel in like body component in the flat position and then observe the amount of discoloration in the surrounding dykem cuased by heat. This concept of how excess heat generated affects surrounding body panel is more easily thought about using the real torch rather then the tig torch. But the effect is still the same nonetheless. In fact you may probaly find that the excess heat from the tig torch actually warps the panel more very local to the patch weld joint owing to the rather focused nature of the arc. Incidently, you will find if you talk to many experienced coach builders you will find that the body rotesserie as marketed by many shop equipment people, is more useful for welding operations of body fab and repair to place the area to be welded into good position than much else. I have been doing this sort of work off and on for "whew" multiple decades. It becomes arduous at times, especially when you work your butt off building this great shaped piece and make a mess of it by welding it into the body. Anymore I am very particular about the fit and the welding position so as to avoid the post welding hammer and dolly work as much as possible. I am frequently amused by the "TV" fabricators fashioning small bike parts and such with all manner of forming equipment. They make it look so easy! I often wonder if these guys have fabricator doubles much like big name actors have stunt doubles. Especially when you watch them welding. Weld a gas tank together for a "Rigid" with a mig welder as they do. Buff off the welds as they do, then mount it as they do. Following that go for a long ride and see what happens. Seen a few of these tanks at my shop, now in Ccolorado, with gas tank mend putty on them looking to be repaired. Get them ready to weld and then put some heat one them and look what happens. Most magically fall apart at the welded seams from poor welding methods and too much grinder massage to correct. Same holds true for body patches. Take the time to get the best results with your welding equipment and skill so that you can go easy with the grinder. You won't have many customer complaints and you won't be redoing your work very often.
If you really want to test your mettle, teach yourself to weld steel body panels and/or patches into place using a Oxy-Acetylene torch effectively forming the "bead" on the backside of the panel. Pays huge dividends in the metal finish operations that follow. You need a really good torch and tips for this however, A well cared for Victor Aircrafter or (my favorite) a Smith's are two good choices for this work. Good regulators with moderate length hoses are also a big help. Recently tried the Henrob torch for this work with good results. Good control over mixture and pressure. However, the ergonomics of the Henrob are uncomfortable for extended use.
Good Luck and have fun! This kind of work will certainly try your patience at first.
XPERTFAB
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