----- Original Message -----
From: Arnold Hite
To: amphicar-lovers@yahoogroups.com
Sent: Thursday, December 25, 2003 7:05 PM
Subject: [amphicar-lovers] Welding Choices
O.K. This is a little off list but I know many of you are skilled
welders. My son and I want to buy a welding unit. I've never attempted
to weld anything. I've always taken my welding jobs to a local welder.
I doubt I will ever attempt to weld on new rear quarter panels, but I
may do small repairs or make modifications to one of my trailers. My
son took a welding class as an elective in college. That makes him the
expert compared to me. The question is what type of welding unit
should we buy? Should we buy an arc welder or Acetylene? Is welding a
thing I can reasonably learn by trial and error? Should I get a book?
Will I need to enroll in the apprentice welding program at the local
tech school? Also if it matters, I have only 110 power in my garage.
Arnold Hite (New Welder want-to-be)
Charleston, SC
Arnold:
I sure don't have ALL the answers, but let me speak to a few points. First, I'm
a very neophyte welder. Many years ago, I had several skilled welders working
for me; unfortunately, I didn't learn any skills from them. OTOH, I did learn
what is a good weld, and what you need to do it. So let's start at the top,
welding at a professional level. BTW, I won't address specialty welding, like
electron-beam. Further, my comments will be toward welding steel (not many of us
have aluminum Amphis).
If you want to weld professionally, there's only two ways. TIG or MIG. Both
processes use an electrical arc which is bathed in a continuous stream of a
shielding gas. The gas (usually a mix of carbon dioxide and/or argon) flows out
of the electrode holder and keeps the arc and molten pool of metal from being
oxidized by the oxygen in the air. TIG uses a tungsten electrode that is not
consumed, and you simply melt the two workpieces together (sometimes melting in
a bit of filler rod if needed). TIG is well-suited to precision work like
sealing the seams on a sheet metal can. Good TIG welding can make a folded-up
box look like a casting.
MIG is the real workhorse of industry. MIG uses a spool of wire, fed thru the
electrode holder. The wire is fed into the pieces to be joined, creating an arc
that melts the workpieces and consumes the wire. MIG can weld 1/2" thick plate
with ease, and a skilled welder can also weld thin sheet metal. MIG can also do
unlimited length beads.
A "stick" arc welder uses a hand-held, flux covered metal rod electrode. You
touch the electrode to the workpiece, and the resulting arc melts the workpiece
and the rod. You feed rod manually and move the stick electrode along the seam
to create the weld bead. The main difference between stick and MIG is that stick
doesn't use the shielding gas. The flux on the electrode rod melts and then
protects the molten metal from the atmospheric oxygen. This isn't a very perfect
process, so it takes decent skill to weld well, and the weld suffers from more
defects. Also, there will be a layer of hard, brittle material (slag) that you
will need to crack off the finished weld. Also, the weld is messier than MIG,
with lots of "splatter". Stick is cheap & quick, but quality is hard to assure.
Gas (oxyacetylene) welding uses a lance-shaped flame to heat the workpieces. A
filler rod is worked into the seam, both to "stir" the two molten metals into
one bead, and to supply filler material. Again, there's no shielding gas, so the
filler rod needs to carry flux. The process puts a lot of heat into the
workpieces, and is slow.
So, it's obvious that MIG is the way to go. An industrial MIG will cost you
several thousand dollars, and will need a 240 VAC supply. Dream on. At the
bottom end of the industrial scale, you can get a MIG for about $350. (Yes,
Harbor Freight will sell you a MIG for a bit less, and I often buy HF tools, but
I don't recommend them for a MIG.) Don't even bother with the "gasless" MIG's;
that's NOT really a MIG. Fluxed wire pushed out of a handle does not make a MIG,
no matter what the ad copy says. Some bottom-end true MIG's will run off of 120
VAC. I suggest that, if you are going to all the trouble to have a MIG, you
should wire your garage to provide a 240 VAC, 40 Amp feed. (You already have
one, if you have an electric dryer. If you need a new feed, get a professional
electrician to do it. Hey, it's not exotic, it's just like asking for a dryer
feed.)
If somebody gives you a stick or non-MIG welder, by all means, play with it. Go
to a metal supply store and ask to buy their debris. Most shops keep a bin right
next to their shear or cut-off saw. They sell this stuff real cheap. (I just
bought two 72" x 6" strips of 16 gauge CRS and two 24" x 8" strips of 14 gauge
CRS for $3.) Just get yourself 50 pounds of odd junk to play with. Practice
clamping it, tack welding, and running beads. Get a feel for how heat distortion
works. Practice horizontal and vertical seams. Stick a welded piece into a vise
and tear the joint apart. Look at your penetration into the workpiece. Do your
welds fail at the edge of the base metal, are the beads as strong as the base
metal?
If MIG is so great, then why doesn't everybody use MIG? As I said, TIG has some
specialty advantages. Non-gas "MIG" entices you with lower initial cost. Stick
welders are the absolute cheapest.
And MIG can't cut. You can only do this with a gas torch. Cutting is obvious;
you heat the metal until it glows cherry red, then squirt a concentrated lance
of oxygen onto it. The oxygen reacts with the near molten iron to create even
more heat, and the immediate area of now liquid steel just runs like water
(actually, the oxygen jet blows it away).
And the MIG can't braze. So what's brazing? It's the same as soldering, just
with different metals. You heat the base (workpiece) metal, slather on some kind
of flux to clean and prevent oxidation, and then melt in a specific allow filler
rod. As the rod melts, it forms an alloy with the base metal, joining the
workpieces. (Notice that unlike welding, you do not melt the workpiece metal,
you just get it hot enough to allow melting of the filler rod.) Brazing can
achieve very good joining of steel, and other metals too.
And now that I've said all that, maybe you wonder what I did? Since I already
had a gas torch kit, I bought a couple of gas cylinders and a cart, and set up
an oxyacetylene gas system. I plan to shape and cut, and maybe tack-weld my
projects, but, for critical structural welding, or for delicate sheet metal
welding, I'm going to call in a professional welder with a mobile welding shop.
Typical cost is about $75 per hour; not too bad if you have everything ready to
fit when the pro arrives.
Please feel free to fill in anything I may have left out, or correct anything
dumb.
Ed
El Cajon
67 Rust Guppy
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