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.
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
That said -
A good book is "Modern Welding" by Althouse. Explains how exactly the arc
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.
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
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 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.
On 8 Jul 2004 08:23:06 -0700, email@example.com (Di De) wrote:
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
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
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
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
of an arc welder. It takes a great deal of skill to successfully weld thin
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
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.
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
to buy an arc welder capable of doing it). Most welding shops will have both
of machines available, and will select the appropriate one for a particular
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.)
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.
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.
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
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.
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!
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