How to weld sheet metal ?

[N.RotaryTech]

So I want to learn how to weld sheet metal.
Some of my projects at home require sheet metal welding, including my FB.
I haven't had much experience with this.
The most recent project I worked on is my Chopper BMX bike. \/
http://i184.photobucket.com/albums/x70/RotaryTech/Other%20pix/017.jpg (http://s184.photobucket.com/user/RotaryTech/media/Other%20pix/017.jpg.html)

That definitely wasn't my best work. That bike is unfinished, still want to do more with it.

I am currently going to school for welding. But at school we are mostly welding on thick metal.

So at home I want to learn how to weld sheet metal.
I have a MIG welder. I think its a "chicago electric 151." It has adjustable WFS with 4 amp settings provided by switches. (Exp. 35, 55, 95, 120 amps) And of course I have a tank with 25/75% gas mix for it.
I also have a "Hobart EZ tig 165i TIG welder with argon tank.

I'm more experienced with my MIG than my TIG. But I figure the TIG is probably more suited to do excellent welds on sheet metal.

The plan for practice is to go to a salvage yard an pick up a trunk lid or hood off a random car, cut it up, weld pieces together.

So dose anyone have any tips/tricks for welding sheet metal with a MIG or TIG?
Amp settings, gas flow rates, spots welds or continuous beads, etc?

[N.RotaryTech]

The reason I mentioned my BMX bike is because the materials I used to extend the backbone are made up of a piece of exhaust pipe and 2 strips of sheet metal.
And I blew a few holes through that sheet metal when I welded it.

[GySgtFrank]

Sheetmetal can be tricky. Weld at very low amps with a low feed speed. The biggest problem with thin sheet is warping. It warps with very little heat. I usually use a wet rag and weld a spot, douse with water, weld the next spot, etc. Very time consuming, but not as much as trying to reshape a body panel after it has been warped out of shape. You will get blow through if you get too much heat concentrated in one spot, so don't keep the arc on the spot any longer than it takes to get good penetration.

[chibikougan]

Bucket wet towels...

[chibikougan]

Get some waste at school and give it a go.. They should also have an outreach program. So you can get extra booth time with an instructor in the evenings..

[Dannobre]

Buy a square of 1/8 or 3/16 copper plate.....use it for backing....

[chibikougan]

Do it!

[Jaco]

MIG is certainly easier and takes less practice than tig for sheet, MIG is a fast freeze process if you will; and if setup right will minimize distortion.

The newer TIG's with pulse can work well, some guys still do it with oxy acetylene so it can be done a lot of different ways. One thing is to practice your filler rod feed, while your watching TV etc you can practice for a smooth steady feed. I can do sheetmetal with TIG but not well- some naturally have a more steady hand than others. Be sure to weld with a sharp freshly ground tungsten and keep your torch really close (usually about the width of the tungsten.)

I'm really experienced with MIG welding heavy structural stuff and do ok with sheet metal. I use .023 or .030 easy grind wire, I run a bit hotter than most and do a lot of short bursts. Only weld 1/8-1/4 at a time depending on the application. Miller Welds has a forum that can be really helpful for specific welding projects. Good luck!

[banzaitoyota]

Check out David Gardenersvideo