Some newbie questions

It transforms high voltage to high amps (current) which loops through your work and electrode to melt the base metal and deposit filler from the electrode.
Depends. 220 for most work over 1/8", sheet metal can use a 110V welder.
6600* F. Hot enough to melt anything in it's way.

This sounds like you *need* to get somebody else to do it...

I Agree!!

Its true! fire resistant coveralls and skin are no match for sparks, grapes, and slag balls....trust me. Having just started my apprenticeship I was told this was only a matter of time.
Sean

If you are really intent on learning how to arc weld then you should get the machine and practice, practice, practice and maybe before practicing, take a local course.
If your small project has to do with the thin sheet metal on your car you are likely to be very frustrated if you are trying to stick weld since it isn't easy to stick weld thin stuff. A MIG would be better in such an application. If the small project is just that then you would be much better off just to have a weldor do it for you.
Billh

By arc, you probably mean stick. For sheet metal on a car, you probably want a wire feed (called MIG) welder. If you are doing anything beyond cosmetic, you would want to pay someone to do it.
That said - 1) A good book is "Modern Welding" by Althouse. Explains how exactly the arc works. 2) Depends on the welder. There are some small 110V welders and many are 220V. The ground cable goes close to the work piece. It isn't really a ground, it's a return cable. If you put the ground clamp on the other side of some electronics / rubber, you are in for trouble. 3) Wicked hot. Will damage things.
Before you do your car, get a lot of scrap metal in a couple of thicknesses (including the thickness of your final piece) and practice. Then practice more.
-Rich

Someone told me that a good policy any time you are welding on any motor vehicle is to DISCONNECT the battery cables. He stated that in addition to messing up the electronics it does something to the battery so it won't last over a couple of weeks. Don't know if he knew what he was talking about or not. Could be an expensive lesson. :-(
Al

"Al Patrick" wrote: (clip) He stated that in addition to messing up the electronics it does something to the battery so it won't last over a couple of weeks (clip) ^^^^^^^^^^^^ There are precautions one needs to take when welding on a car. Protecting the battery in the manner described sounds like BS. I put it in the same category as the old wives tale that putting a battery on a concrete floor will cause it to discharge.

An even better policy is simply to put the ground as close to the weld as possible and degrease/grind/sand as necessary to ensure good contact for said ground. Electricity will take the path of least resistance.
As a previous poster mentioned, the return path should not go through any electronics, bearings, etc. It should be as direct as possible.
Jeff Dantzler

Basic arc welders are boxes with a big transformer inside. This transformer steps down mains voltage to an open circuit voltage of roughly 70 volts, and an arc voltage of roughly 20 volts. (The transformer reactance is designed so that the voltage sags this way between no load and full load, this is called a constant current characteristic.) You need the high open circuit voltage to strike the arc. You need the lower voltage to maintain the arc.
While stepping down the voltage, the transformer steps up the current (that's the way transformers work). The amount of current in the arc basically determines the amount of heat delivered to the object to be welded, which in turn will be determined by the thickness of the metal being welded. The welder will have some sort of control which allows you to set the desired welding current (basically it does this by lowering the full load arc voltage).
This can be a rotary switch that changes taps on the transformer, a series of jacks you can plug the electrode cable in for different currents, a movable iron slug to change transformer reactance, or some sort of electronic control. Any of those methods work, and different welders will use different methods. The more desirable methods are electronic control or the movable iron slug because they give you infinitely variable control.
Some arc welders are AC only, others are AC/DC. DC welding current is generally preferred, but machines with DC capability generally cost more.
After you have adjusted the machine for the desired welding current, you strike an arc between the consumable electrode and the work piece. Then the fun begins. You have to maintain a constant arc length as the consumable rod burns down, you have to move along the joint, and you may have to weave the tip, all at the same time, and all in such a way as to precisely control the welding puddle. This requires good hand-eye coordination and a lot of muscle memory skill. Like learning to play the guitar, the only way to learn to arc weld is to practice. It takes time, and it helps enormously if you have a skilled instructor watching you and telling you what you're doing wrong. A decent arc welder will require 220 volts, the 110 volt cheapies are mostly a joke. You'll need a minimum of a 30 amp circuit, a 50 or 60 amp circuit will be required if you want to weld heavier material (greater than about 1/8th inch thick). The welder's ground cable clamps to the work piece you're trying to weld. It completes the circuit from the consumable electrode back to the welding machine.
The "sparks" are bits of molten metal. They are *very* hot. The arc temperature approaches 10,000 degrees (Fahrenheit), and the molten drops of steel will be at least 2700 degrees (probably a lot hotter as they leave the arc zone). They cool quickly in air because they are small, but they can still produce burns on exposed skin, or set any flammable materials in the area on fire. The work piece will get very hot too, and even after it stops glowing, it can still burn you if you touch it. Also, the arc produces ultraviolet rays which can damage your eyes and your skin.
You must wear suitable protective clothing (helmet and leathers) to prevent both thermal burns and arc ray burns. Please do *not* follow the very bad practices demonstrated on such shows as Monster Garage or American Chopper. Those people are asking for eye damage, skin cancer, and nasty thermal burns. It may take 20 years for skin cancers or cataracts to form from the welding exposures their unsafe practices produce, but their folly will catch up with them.
Now I don't want to overly scare you. Using proper safety equipment and practices, welding can be a very rewarding and safe activity. But this is one activity where you *really* want to know what to do and how to do it, or the consequences can be serious.
I certainly don't want to discourage you from getting a welder and learning how to use it. But from the level of the questions you are asking, you'd benefit greatly from first taking a welding course at your local community college or technical school. It is *hard* to teach yourself to weld without expert instruction and constructive criticism, and there are safety issues about which you *must* become informed for your safety, and the safety of others.
Final note, for auto body welding you'll typically want to use a MIG welder instead of an arc welder. It takes a great deal of skill to successfully weld thin sheetmetal with an arc welder (you'll tend to either burn through or not get a good bond). A MIG makes it easier, and faster, and produces a smaller HAZ (Heat Affected Zone) in the metal around the weld, which will reduce the amount of warping you'll suffer when welding sheetmetal.
A MIG is somewhat easier to learn to use, too, though you need to be wary that a MIG can produce a pretty weld that is *not* sound, called cold lap. Any good looking weld you make with an arc welder is likely to also be a strong weld. That's not the case with MIG. Again, expert instruction can be a huge help in learning to use this welding process.
Note that it takes a big, powerful, and expensive, MIG machine to weld heavier steel. That's better done with an arc welder (or at least it is significantly cheaper to buy an arc welder capable of doing it). Most welding shops will have both types of machines available, and will select the appropriate one for a particular welding job. (There's also TIG welding and gas welding for more specialized welding jobs around an auto, and increasingly, plastic welding using a static hot air source. One process isn't best for everything, though you can do a lot with a small MIG, or a 200 amp class arc welder.)
Gary

Another note is that on modern unibody cars made with high strength low alloy steel, MIG is the only choice for welding. This is because of the smaller HAZ like Gary mentioned. Some vehicle steel (like heat-treated frame members) cannot be welded at all. You need to know what kind of steel you are repairing.
Older cars can be repaired by a wider variety of welding processes.
I've done some repair work on vintage VW's using a small tip on an oxyacetylene torch. Gas welding is great practice for the other welding methods because you learn to control the molten puddle.
Like other posters have mentioned though, MIG is the prefered process for auto body work.
Jeff Dantzler

Would brazing be ok for this? For some odd reason (getting old, probably), I've hung up the mig for good, and mostly enjoy ox/acy and stick welding like I started with....Of course, I don't do production stuff:)

Modern autobody repair is not my area of expertise so I will defer to those that know more.
HSLA unibody frames rely on the integrity of the frame as a whole unit (hence unibody). I would be extremely hesitant to braze say 2 panels together that may have a significant structural load on them.
The old cars I've worked on were mild steel. The German manuals actually had tips for gas welding repairs i.e. short stitch welds / trying to minimize heat input/etc.
Wish I could be of more help.
Jeff Dantzler

While brazing may technically work for lap joints, I wouldn't recommend it for several reasons. The HAZ will affect modern HSLA steels, and brazing by its nature produces a large HAZ. If you do decide you need to weld after all, the copper will contaminate the weld zone and make getting a good weld impossible.
Lap joints in most cars are spot welded (which you can simulate with MIG plug welds), not seam welded. Brazing isn't suitable for sheetmetal butt joints, which make up the majority of the seam welds in panel repair.
Gary

Wow, Gary....Did you just drink a whole pot of coffee or something? That was like the first two weeks of the local welding program! I hope you didn't waste a bunch of time on a troll. Very informative nontheless!

"Jeff Dantzler" wrote
My dad ( born in 1918) said they used to use a torch and baling wire or coat hangers to do the fenders on their Ford Model A's and T's.
OA works for lots of stuff.
STeve

"Jeff Dantzler" wrote
When you compare the HAZ for OA to MIG, you understand why MIG is the preferred method.
(HAZ is the heat affected zone. Look at what discolors. That is the HAZ.)
Steve

Actually, I did drink a bunch of coffee. :-)
I like to give as complete an answer as possible to this sort of question. It ultimately saves time.
Gary