i can't see it. why?

I've taken apart a bunch of batteries for this step and none of them have carbon rods in them, just a nail on the negative end and some bluish powder in a cardboard cylinder on the positive. How old were the batteries you were using? I did find a rod in an old hobby battery I had but its huge

A couple of things. One, Oxy-fuel glasses are usually around a shade 5, and with any arc welding, a minimum of atleast shade 7 is suggested (straight from textbook.) Goggles and shaded lenses are very inexpensive. There is no reason not to be safe when it comes to your eyes.

Also, you probably should use some kind of flux on your joints. An unprotected molten pool will absorb moisture and atmosphere, causing porosity and oxidization. (This is probably where your welds are breaking)

rough science
this is the PBS website. unfortunate I own the DVD so I can't send you a link to the the video and for some strange reason my computer won't let me clip it out.
BTW the show is right up the alley of this site. a bunch of scientists in the middle of nowhere having to build stuff with what they can find.

Hello!  Thanks for the idea!  Soo many things you can do with a trainset transformer.     

Afew questions... 
1> Are you using the ac or dc output from the transformer?
2> What concerns are there for safety?  (rubber matt to stand on?  don't touch the electrode? ect..?) 
3> Do you think i can use a regular 3/32 e6011 electrode and still get a decent arc?

Thanks again!  I give you stars!

cool! this seems like a potentially cheap and non-threatening way to get an idea of what welding is about. i may have to try this! regarding the pencil "lead" for carbon rod discussion, i'm guessing that the softness/hardness of the graphite might make a difference. hard leads are mixed with fillers like clay to obtain their degree of "hardness". a harder lead leaves less on the paper, where a "softer" lead is more purely carbon/graphite and leaves a darker mark. i'm guessing that a 6B or 8B might work better for arc purposes than an HB or a 4H, for instance. might be worth a trip to the art supply store for experimenting for those so inclined. anyway, interesting instructable, LinuxH4x0r. thanks for sharing!

Can alsi be done using your car battery.

How many amps is this?I want to know how many amps it takes to weld 24g metal.(my dad has a roll of the stuff)

would a transormer from a microwave work?

What does the carbon rod do? I know they are typically a small point of short where it causes the tab to melt to fuse but just trying to figure out why that's used. I am semi-considering replacing the batteries of a laptop and I know the tabs are arc welded on and its preferred to weld rather than solder to avoid excess heat. The hard part is finding a good power supply for this. I had an Antec that didn't have any protection on the 5v rail, first time I made a wire turn red and melt! I see 85watt, what voltage does the transformer output at?

Somebody made a similar instructable, it was DIY cold heat soldering. The guy suggested using some strong amperage power supply (like my old dead pc power supplay, rated at 15amp (!) ) some thick wire (obviously; same as here) and, the fun part, the carbon rods were mere thick pencil leads. Pencil leads are actually made mostly of carbon, depending on the brand I guess. Perhaps if dismantling a battery is not possible, one could consider thick pencil leads? I've bought some 0.9mm leads from Steadler, found in any decent art supply store and business supply store.

I saw this on rough science. they used it to melt gold.

LinuxFamily'09 I haven't thought of a slogan yet(I'm serious)

cool...I will be trying this soon! Also need an inexpensive way to weld aluminum.

get some welding goggles if you're gonna be doing this often, the uv and infa red light can really screw up your eyes over a long period of time.

I remember when Spock used this method to get him and Kirk out of jail on the Nazi planet. You copycat! LOL. just kidding. Good work!

I have a welder and it is amazing how many times I want to weld thinner material rather than thicker items. This could be very useful to someone with occasional needs and a limited budget. An alternative I have used is to braze with a MAPP gas torch. It works with thinner items if the heat does not damage something you want to keep cooler.

Awesome!
^{*whut can i doez with 24g metal?*}

. Nice job.

woooooo, awesome, hey, just one thing, change thinker to thicker in the first step... voted, fav'ed, and 5-stared, this is nice...

Nice! I can't believe I missed this instructable before. I guess your shameless plugging worked out. You've got my vote!

I guess you should specify an insulated handle pair of pliers. You know some geniuses only have a pair of slipjoint pliers or maybe that vise-grip to work with. I'd also hook that up with a piece of insulated wire to the power pack. Or does it only short out at the carbon rod tip?

I've never welded but probably a good idea to do this outdoors or an open garage/shed to dissipate any fumes that are produced.