Hi Folks. Thought I might throw out a few things I've learned to fellow
novices in the group, who might be thinking about learning to do some
welding/brazing. The veterans know all this and way more than I do
about it.
You can save a ton of money and time (and begging pro shops to do it) by
getting your own gas torch setup. The torch is sort of passe' today for
most pro welding, I gather, because it's too slow and puts too much
heat into the metals and causes too much warping. Mig and Tig, etc.,
have replaced it.
But what it remains very useful for is building exhaust systems, coolant
pipe systems, and tacking larger fabrications together to carry them to
the pro welding shop in one piece so it is the way you want it. The
pros will respect you for it and charge you a whole lot less to finish
it. I did my whole SCTA spec roll cage this way with a hack saw,
Speedway joint jigger and a half round file.
National Welding Supply is a nationwide chain that sells a nice little
"farm and home" torch set which is pro quality in all but the external
finish, uses the same tips, valves, gauges, etc. They also sell and
exchange the small tanks you want for home shop use that are easy to
lift and carry in your trunk(carefully!), but hold plenty for a lot of
welding. None of the above is very costly, and a friendly salesman can
help you get started in the right direction.
Obviously, the torch can be dangerous, you can injure yourself and set
your shop on fire if you are careless about any exposed gasoline vapors,
oily rags, oily gloves, etc. You need the right goggles to protect your
eyes, covering for your body parts to avoid burns from sparks. DO NOT
EVEN PICK UP THE TORCH, unless you have ALL the safety considerations
covered. The oxygen tank has 2000 psi in it so if you drop it and bust
the valve off you may have a 25 pound bomb flying all around your shop
for a while. Just for one example. Adequate ventilation is essential,
too. You can get half a dozen 'fire bricks' (fireplace bricks) for a
workstation from a good builders supply yard.
Anyway, you get your equipment carefully hooked up and checked by the
book, crack the acetylene valve and light the tip (I use a 00 tip for
exhaust pipe work) with your spark gadget, then adjust the oxygen valve
until you get the right feather of flame. I was taught to adjust the
flame a little fuel-rich, leaving a little visible cone of the
fuel(acetylene), because an oxygen-rich flame tends to burn the steel
when welding, causing it to break later. For every thickness of steel
you need a different heat of flame, hence the variety of tip sizes
available. And with the same tip you can adjust your fuel and oxygen for
more or less heat. In general, you want a flame that does not 'hiss'.
When welding exhaust pipe material, for instance, if you have too much
heat the steel melts before you want it to. Not enough heat, it takes
too long to get hot.
Exhaust pipe low-carbon steel is available at NAPA stores in sticks
everywhere, and at other serious auto supply companies. Headers by Ed
also sells it mail order, Ed has everything conceivable you want, and
gave me good service. You can make any shape or size of exhaust pipe by
cutting and joining straight pieces and pieces of U-bends. When cutting,
fitting and tailoring the pieces you tack them with three or four spot
welds before finish-welding one piece at a time. This steel is easy and
(almost) fun to work with. Flanges are available individually or in one
piece for V8s, but the technique here is a little more challenging. You
can't just butt-weld a pipe on the outside of a flange, it will probably
break off from vibration before long. The pipe must go inside the hole
and be welded carefully on the head side of the flange, then brazed into
the hole from the outside. You get a strong but slightly flexible joint
this way that will last. I use a special high-temp brazing rod for this
particular job, considering the temperature you get here. Warping
always occurs more or less with these flanges, so 5/16, 3/8 or thicker
plate steel works better. If you can't break a completed exhaust pipe
with your hands, the joints are probably ok.
Before any successful welding or brazing, the steel must be thoroughly
cleaned with a serious wire brush. I use an agressive knotted wire
brush in a bench grinder. Always use a face shield! And gloves. The
actual welding joint consists of two surfaces with the smallest possible
gap, that have been brought in a controlled fashion to the steel melting
point. Your 1/16" steel rod is added, and the three items melt together
as you watch, into a nice bead. The strength of the joint is entirely in
the quality of this bead. You can weld any amount of exhaust pipe tubing
from this simple basis. A bit of practice and you get the knack fast,
when you
WANT to do it. One other trick an old-timer told me, is after you get
your pipe constructed with your strong beads, wire brush your beads and
go over them with the torch to bring each bead to blue heat. For some
reason (maybe the carbon added by your acetylene) the beads tend to be
hard, but the bluing softens them back to the hardness of the pipe
material, so you have a more uniform structure. If you don't do this
the weld areas may crack later in service. Brazing, by the way, is not
satisfactory for butt-joints on exhaust pipe tubing. They have to be
welded.
For coolant pipes I use 1-3/4" exhaust pipe tubing and here I prefer to
braze them with nickle-silver brazing rod which is even easier than
welding. Cleaning the steel is the same, but here the correct flux is
used with the rod, and the steel is only brought up to a yellow heat,
not to melting point. When the steel gets up to the yellow point,
you'll see the rod just jump onto it, forming an intermolecular bond
probably as strong or stronger than the steel itself. With brazing you
go over it twice with the torch, to 'tidy it up' as the Brits say, melt
it down more evenly. With welding or brazing you have to go over the
joints with your wire brush to get rid of 'detritus' before painting.
The brazing flux leaves a black glassy residue, best removed by tapping
with a ball peen hammer (eye protection!) and your wire wheel. Leak
test your coolant pipes with a big rubber plug (hardware store item) in
the end. If they don't leak when you fill them with water then, they
probably won't leak later, brazed up with this good material with good
cleaning and the right flux.
Other novices will benefit as I do from a copy of Ron Fournier's "Metal
Fabricator's Handbook".
Comments from the veterans? Regards, ArdunBill from Chesapeake, VA.
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