Gettting a tig welder isn't in the forseeable future but I can work with the welder if I knew what to tell him. The shop is mostly fabrication of mine machanery and they use the tig for angle iron. Could you share a little knowledge as to what works best?

Is there a basic heat you work with for guns?
Does the metal have to be preheated?
WHat do you use for a filler?

The welder tried using a piece of his mig wire for a filler rod and I don't remember what is was but it was impossible to file. Would it be better to have a small groove and no filler or a larger groove and a filler?

thanks in advance
dale