From: highflyer <highflyer@alt.net>
Newsgroups: rec.aviation.homebuilt
Subject: Re: Welding torches
Date: Wed, 09 Sep 1998 08:30:34 -0500

KBoatri144 wrote:

> I'm considering a Hatz as my next project, so I'm interested in melting
> pieces of metal together....
>
> In the Sport Aviation I received  today, there was a lengthy article pushing
> TIG welding.   What are the advantages/disadvantages??
>
> KB

The arc you get with the tungsten electrode provides a very concentrated
heat source.  You can fine tune the heat with the thumb or foot control.
You weld with it exactly like you do with gas.  The torch just provides
heat.  For welding you build a puddle, nurse it along, and cool it down
at the end.

It is a little faster than gas welding because of the higher heat.
They usually recommend that you start out with gas to learn to weld
with TIG.  It saves some fiddling around on welds.  You use the same
filler rods that you would use with gas.  I use ER70S-6 instead of the
ER70S-2 that they recommended in the article.  My TIG system cost
about $5,000 new.  Now, much used and several years old, it still goes
for around $1500 if you can find one.  It is a Miller system.  Even
after welding it with TIG I have to get out the torch with a big
rosebud and normalize around the welds so they won't crack.

Most of the time I just get out the O/A tanks when I have a little
welding to do.  It is actually pretty quick and easy.  Like TIG, it
doesn't change much with material.  Just adjust the heat for the
material, use the correct filler rod, and get the flame properly
adjusted so you don't either oxidize or carbonize.  With gas I can
normalize as I weld and I don't have to come back later and do it.
This doesn't actually save TIME, but it is convenient.

For a newbie planning on building one airplane I never could understand
why they were so anxious to spend $1500 for a TIG rig, when they could
just as easily do everything they want to do, and then some, with a
good O/A rig.  I bought a first rate O/A setup at a yard sale for
$50.00.  A new system can be purchased for about $250.00 and be top
quality.  Don't be blinded by the technology.  I wouldn't change
until it does something for me that is worth the cost.

I have a TIG rig, but I wouldn't if I had had to pay as much as $1500
for it.  I got mine on indefinate loan from a friend who used to have
a professional welding shop and can't bring himself to sell his best
piece of equipment, just in case.  I understand that motivation.
Also, the TIG rig does provide a first class stick welder that I do
use around the hangar.  I don't use it on airplanes, but I used it to
build the hangar and the hangar door system. :-)

From: highflyer <highflyer@alt.net>
Newsgroups: rec.aviation.homebuilt
Subject: Re: The Unnecessary DC Cheater
Date: Wed, 14 Oct 1998 09:08:32 -0500

Bob U. wrote:
>
> >>
> >What's a $DC$ welder ?  I paid the princely sum of $106 for
> >my Hobart in 1980.
> >
> >Ray
> ++++++++++++++++++++++++++++++++++++++
> What's the catch?
> Tell us the rest of the story, Paul Harvey!

That is about what they cost then.  I paid $190 for a Forney AC-DC
buzz box in 1994 at the local hardware store.  It is an excellent
buzz box and offers all of the advantages of a DC welder.  Is it
useful for building airplanes?  No.  I could use it for welding up
a jig or something.

However, I  have access to a Miller Pipeliner
TIG rig also that does everything the stick welder does and also
almost everything else you might want to do with a welder.  Of
course, they now cost about $1500 second hand.  Is it useful for
building airplanes?  Not really.  I can TIG a fuselage, but it
is NOT any easier than welding it with my O/A rig, and I still have
to get the O/A rig out to normalize it after I am done.

My O/A rig cost me $50 at a flea market.  I also spend another $250
for a lifetime lease on the bottles, so I don't have to pay the
$3.00 monthly demurrage on the gas bottles.  EVERYTHING you would
ever want to weld on or for a homebuilt airplane can be welded with
this rig.  I even welded up much of my HANGAR with this rig.  It is
by far the best way to weld aircraft type things.

I do have a MIG wire feed welder.  It is really cute.  It is sort of
like welding with a ball point pen.  It is totally worthless for any
kind of aircraft welding, but it is worth its weight in persimmons
for welding up truck bodies.

hf

From: highflyer <highflyer@alt.net>
Newsgroups: rec.aviation.homebuilt
Subject: Re: Wire welder
Date: Fri, 23 Oct 1998 09:59:41 -0500

rabue@my-dejanews.com wrote:
>
> I've been fighting this for a long time, but think that I will buy a wire
> welder tomorrow night.  They've finally got them down to where I can run it
> on the 1937 wiring that I have in the house.  My question is, does anyone
> have any experience with the Century wire welders?  Would the gas-less
> version be ok for 4130 or would the next one up be a better choice?  I don't
> have a lot of choice, the service into the house is only 50 amps, if I am to
> believe the fuses in the basement.  I only have one 20 amp circuit in the
> house, and that's in the livingroom for the air conditioner.
>
>

In my opinion, NONE of the wire welders are "OK" for 4130.  Especially
if it is going to become part of an airplane.

There are two welding processes that work well for aircraft welding
and will give an aircraft quality weld with a suitably trained
person doing the welding.  These are TIG ( also called "heliarc" )
and gas welding ( Oxygen/Acetylene ).  Both techniques require a
normalization process after the weld is completed to restore the
ductility and toughness of the 4130 steel in the vicinity of the
weld.

It is generally recognized that the best way to learn to weld
with a TIG outfit, is to start first with O/A.

You need either an O/A outfit with a rosebud or a large high
temperature oven, to perform the normalization process after the
welding is complete.

A complete O/A setup can be had for about the price of a fair
quality buzz box transformer type stick welder.

A workable TIG outfit will generally cost from $1500 upwards.

I see no reason for any homebuilder to fool with anything but
O/A welding for a homebuilt.  It doesn't really take a LONG time
to acquire the skills to perform aircraft quality welding with
an O/A setup on 4130 tubing.  About forty hours of good directed
practice should make you a pretty competent O/A welder.  This is
especially true if you take the time to read something like the
O/A Handbook from Linde or other accurate welding manual along
with the directed practice.  It should not take you more than
five minutes to learn how to adjust the flame.  The tip selection
is also stone simple.  If you don't get a puddle started in the
time you can comfortably hold your breath get a larger tip.  If
it melts instantly and tries to blow away, get a smaller one.

Form a puddle and practice moving it about with the heat.  Add
metal to the puddle by melting the filler rod ABOVE the puddle.
Do NOT stick the filler rod INTO the puddle.  Learn how to control
the size of the puddle.  The thicker the metal, the bigger the
puddle you require.

Learn how to move the puddle.  The more slowly the puddle moves,
the deeper the puddle gets and the greater your "penetration" is
for the weld.  If you move too slowly, it goes all the way through
and you puddle runs out through the resulting hole.  Oops.  If you
move too fast you get a pretty weld but it doesn't penetrate deeply
enough to fasten the pieces together.  You can usually see this by
looking at the edges of the weld bead.  If the weld bead flows into
the pieces welded smoothly with no bump you are doing it exactly
right.  If there is a hollow that climbs UP to the untouched surface,
you are going to slowly and not running the puddle full enough.
If there is a high bump dropping down to the untouched metal you
probably do NOT have penetration and your bead is just stuck on top.
This last is the most common problem with "wire feed" MIG type
welding operations.

A decent O/A rig is NOT expensive.  My gauges cost me about $25 at
a flea market.  My welding torch was about $80 years ago at Sears.
Look for a lightweight torch that is not real large and is easy
to manipulate into odd positions.  I personally prefer the ones
that have the adjusting knobs to the tip end of the handle instead
of at the BACK end of the handle where they are hidden by my
wrist.  That is a personal opinion and many people weld very well
indeed with either type.

I would not waste the money on any electrical welder for building an
airplane.  Now if you have other welding jobs in mind, fine.  Do not
use it to build your airplane until and unless you are good with TIG.

highflyer

From: highflyer <highflyer@alt.net>
Newsgroups: rec.aviation.homebuilt
Subject: Re: help! MIG welding Chrome Moly?
Date: Wed, 02 Dec 1998 11:57:18 -0600

Lee McGee wrote:

> Well then HF, you would not want to fly in any Citabria, Decathlon
> or Champ either, even a brand-new American Champion one.  They do not
> post-heat-treat their MIG welds.

Sorry if I seem to be picking on you Lee.  I am not.  However, I am
extremely reluctant to do any serious flying in the brand new American
Champions because of all the problems I have heard about and seen with
tubing cracking and breaking next to the welds.  I do fly an Stinson
108, that is currently disassembled in my hangar, even though its
fuselage was electrically welded.  Not with MIG either, it was done
with a good old fashioned DC buzz box!  However, they did run the
entire fuselage through an oven heat treat afterward to restore the
strength of the tubing near the welds.

> I have flown in plenty of Citabrias and they are great!  I have heard
> stories about Citabria weldment failures in the aft fuselage/tailwheel
> area, but this is an area which takes a lot of abuse, and that is
> almost probably a common repair on older airplanes that have seen
> hard use.

I too have flown in plenty of Citabrias.  I am not quite so enthusiastic
about them.  I flew airshow routines in the darn things years ago and
it is one of the best excercises I ever did for arm and shoulder
development, at least for my right arm! :-/  I also rewelded the
frames on them more than once.

> BTW all of the major structural work of my current fuselage
> structure is traditionally gas-welded, as I bought it from another
> builder.  Would I mig-weld an entire fuselage if I had to, knowing what
> I do now?  Probably not, it is hard to control and get right.  I don't
> have any qualms about the arc welding, however.

Exactly.  It is hard to control and get right.  At the same time, gas
or TIG is relatively EASY to control to get right.

> Yep, don't get a cheap Mig welder.  I use a Miller (130), Lincoln
> (SP125) is also a class act.  These are the best there is
> in small MIG welders.  Red or blue?  Do *not* use a Home Depot
> $300 welder on an airplane!  WIth my Miller you can really tell that
> you are getting the heat into the weld and the penetration.

For sure you don't get a cheap MIG welder.  The electric welder that
I use, which is NOT mine, but belongs to a friend who works with me
a lot, is a big old Miller  unit.  I cost about $6000 and does the
job quite nicely.  The little Lincoln SP125 or Miller 130 will both
do a credible job given appropriate operator expertise.  However,
it is STILL much easier to do aircraft quality welding with gas or
TIG.

> Finally, I would guess that many welds that have been "normalized
> with a torch" have been heated in a fairly uncontrolled way; I bet these
> areas are more annealed than you would expect from 4130N, so also weak
> but in a different way.  If I'm not expecting a lot of shock on a welded
> area I'd prefer to leave it untreated, rather than screwing it up
> by annealing it in an amateur manner.  I've tried this and beat on
> the pieces to see which breaks first!

Normalizing is not annealing.  They are similiar processes but are
different.  I have heard that argument many times.  All I know is
that when I welded 4130 and didn't normalize it afterward I often
had to reweld it when it cracked alongside my weld.  When I took the
time to properly normalize it afterward I never had to reweld it.
That convinced me.  I don't know whether it is "more annealed" than
I would expect, but then don't crack.

All of the production aircraft with mig welded fuselages also have
problems with cracking of the tubing.  Normalized 4130 steel tubing
does NOT crack.  It will elongate significantly, deform tremendously,
and then tear.  It does NOT crack without a great DEAL of deformation
prior to the rupture.

HF

From: highflyer <highflyer@alt.net>
Newsgroups: rec.aviation.homebuilt
Subject: Re: help! MIG welding Chrome Moly?
Date: Thu, 10 Dec 1998 10:29:02 -0600

rabue@my-dejanews.com wrote:

> O-ring, Bruce, and HF,
>
> Bruce made the point that this is a subject that has been pounded into the
> ground.  IT NEEDS TO BE! Then it needs to be dug up and pounded again.  It's
> important!  What else is important is that there is always more than one way
> to achieve a satisfactory end to a need.  Another thing that needs to be
> brought out is that 4130 is nothing more or less than a lower grade of
> chrome-moly steel, and other than carbon content is no different from the
> other 41XX steels. It does not harden as readily as 4140 or 4150, which is
> why it is used in aircraft, the other two would be far too brittle.  It is
> not a "magic" material, nor does it have any qualities that make it too far
> different from any other chrome-moly.

I agree, and that is why I continue to answer questions about welding
on aircraft tubing rather than referring folks to Deja-News or the
FAQ.

I agree that 4130 is NOT anything special among the family of chrome
moly steels.  It happens to be a good one for aircraft use.  It is
also interesting to see how the strength increases when it is
"normalized" and instructive to see how the "normalization" temperature
differs from the recommended temperatures for "tempering."

In my experience, all steel with any significant amount of carbon in
it can easily embrittle next to a weld.  I welded and rewelded many
structures before I realized that even a little bit of carbon made a
difference.

As with any higher carbon steel, heating past the transition temperature
and then quenching will "harden" the steel.  The percentage and quality
of the grain level changes that cause the steel to harden depends a
great deal on the speed of the quench.  An air quench is slowest and
generally gives less hardening than the more rapid quenchs.  A water
quench is probably the quickest because water pulls a LOT of heat
out quickly when it changes state.  Water quench will harden any
moderate to high carbon steel quite effectively.  Sometimes too
effectively.  The faster the quench and the thinner the section the
more likely warpage will mess up your job.  Oil quench is a nice
intermediate quench.  It is faster than air and slower than water.
It is used for many steels where dimensional stability and lack of
warpage is important, even though it won't usually "harden" quite
as much.  With the hard comes also, unavoidably "brittle."  Hard
steels will crack and chip before they bend or deform.

This "brittleness" can be alleviated by a "normalization" or a
"tempering" process.  Both of these processes are similiar, differing
only in degree and not in kind.  This ability to bend or elongate
before breaking is called "toughness."  Normalizing or tempering
"draw down" the hardness, increasing the toughness.  Like everything
in aviation, it is a compromise.  You give up hard for tough and vice
versa.  The normalized state for 4130 alloys is a nice compromise.
The remaining hardness allows a significant increase in strength
while easeing almost all of the brittle.  It is several times as
strong as the "annealed" or "soft" state, but still will give and
elongate a lot before it actually breaks.  Perfect for structural
applications.

Welding thick sections would probably not cause a problem.  However,
a quick weld on thin wall tubing is a different matter.  Most aircraft
are constructed of tubing that is between .030 and .050 inches thick.
This is really quite thin.  Thin sections lose heat more quickly than
thicker sections.  When you weld metal you have to bring the metal
in the joint to the point where it melts and runs together.  Since
the transition temperature required for hardening carbon steels is
always less than the melting temperature, there is always a region
near the weld where the "hardening" temperature was reached.  A
quick and precise weld, like TIG or MIG, will heat a narrow zone
quickly to the molten point.  Since the heated region is very small,
it also cools quickly, by radiation, by conduction to the air, and
by conduction into steel a short ways away from the weld that was
NOT heated.  This rapid cooling near the weld acts line a quench and
causes a narrow hardened region to form alonside the actual weld.
This region is quite brittle and will easily crack unless the weld
itself is "normalized."  This can easily be done with an O/A torch
because the "normalizing" temperature range is fairly large and is
easily identified by the "red" glow of the steel when it reachs the
correct temperature range.  This temperature is commonly referred to
as "red hot."

The welding process is totally independent of the means of heating
the metals at the joint.  Anything that gets them hot enough to melt
and flow together will create a weld.  The appropriate penetration
is controlled by controlling the depth of the molten puddle.  In
welding, ALL WELDING, the control of the molten puddle is the key to
strong and consistent welding.  When you learn to read and control
the puddle you know how to weld.  I repeat, it does NOT matter where
you heat comes from.

However, with moderate to high carbon steels in thin sections, the
way the heat is applied and removed and the rate of removal can be
critical to the quality of the weld.  It is also quite easy to
OVERheat the puddle and literally burn the carbon out of the steel.
Either burning carbon out of the puddle, or using a smoky flame and
ADDING carbon to the puddle, can result in a change in the alloy
when the puddle cools and a resulting major change in the strength
characteristics of the metal within and near the weld.

O/A allows careful control of the puddle and the puddle temperature
by simple manipulation of the torch and the distance of the puddle
from the tip of the inner cone of the flame.  The welding equipment
is the least expensive and the materials cost is quite low.  It
allows for easy control of the rate of application of heat and, more
importantly, the rate of removal of heat after the weld.  Aircraft
welding requires a little practice controlling the puddle, but is a
skill that can be easily learned by almost anyone with a little
proper direction and a few hours of practice.

TIG also allows careful control of the puddle and the puddle
temperature, by manipulation of either a foot control or a finger
control temperature adjustment.  The welding equipment is relatively
expensive but the materials cost is quite low.  It does allow for
very precise control of the heat and the puddle, but does not work
well for broad area heating or heat removal rates.  Generally TIG
welds should be "normalized" after completion with an O/A torch or
with an oven large enough to heat the entire structure to the
"normalizing" temperature of "red hot."  Aircraft quality welding
with TIG is not too difficult for anyone who has learned puddle
control with an O/A torch.  You have to learn the temperature
control by finger or foot, rather than by changing the distance
from torch to joint.

MIG allows the least control of the heat and the puddle.  Temperature
control is usually varied by stopping the weld and changing the setting
on the box.  The filler rod/wire feed rate is constant and you vary
you puddle size by varying your rate of movement along the weld.
The puddle size varies the penetration.  Moveing too slowly will
blow holes through the tubing.  Moving too rapidly will lay a nice
bead on top of the metal without any strength that results from the
depth of penetration.  The constant rate of heat application does
not allow normalization at the time of welding, and does require that
the welds be heated to the "normalizing" temperature either with
an O/A torch or in an oven large enough to hold the entire structure
and bring it to a "red heat" for normalization.

THEREFORE, I SEE NO REASON for a HOMEBUILDER, who is going to weld up
ONE fuselage, to invest in BOTH O/A equipment for the required
normalization process and some other more expensive technology for
doing the actual welding itself.  Since the O/A equipment is needed
in any case, and it is ALSO the easiest technique to learn and apply
for the actual welding, why spend the extra money unless you DO have
a production line and plan on welding many fuselages.  Then the time
savings realized by the electrical welding processes can be beneficial.
If you, like most homebuilders, have more time than money, don't fool
around with the electrical stuff for welding up your airplane.

THAT IS NOT A "MY WAY OR NOT AT ALL" attitude.  It is a carefully
thought out recommendation based on an analytical comparision of the
commonly available ways to stick metal peices together and still
retain a modicum of strength.

I find it personally offensive that you would characterize my
carefully thought out advice, based on both theory and practice over
many years, as some kind of pejorative exhortation to throw away
your little black box.

As I believe I mentioned, the MIG unit is excellent for general purpose
welding applications.  It is considerably LESS excellent for welding
up 4130 tubing structures for aircraft.  That is the way it is and is
NOT a short sighted and conservative gut reaction.

HF

From: highflyer <highflyer@alt.net>
Newsgroups: rec.aviation.homebuilt
Subject: Re: Filler rod for gas welding 4130N ???
Date: Wed, 30 Sep 1998 14:30:50 -0500

Dreidjax wrote:

> Iam soon to be welding up a fuselage for a Pober Pixie.
>
> Been using "Airco #7" 1/16" mild steel filler rod, but have not even tacked
> anything on the airplane with it yet.  I understand there is a growing
> preference to the 4130 filler rod for this purpose. I havnt used any yet. Any
> thoughts?
>
> Does this rod perform similiar to mild steel? Puddle workability about the
> same?...or dramatically different? Easier to use?...or more difficult?  Heat
> control about the same?
>
> Would like to hear any thoughts or comments.


You want a low gas, low hydrogen filler rod.  4130 filler rod is
available at a relatively high price.  It does work.  However, the
carbon content of the rod tends to increase during the welding
process unless your flame adjustment if absolutely perfect.  The
result is some brittle welds with the 4130 rod.  The ER70S-2 or -6
rods, on the other hand, make a nice smooth puddle with very little
outgassing and make a smooth  strong weld that normalizes nicely and
maintains the strength of the tubind quite adequately.  Remember you
always have a lot more metal in the weld, and much of it is melted
4130.

From: highflyer <highflyer@alt.net>
Newsgroups: rec.aviation.homebuilt
Subject: Re: BRUCE FRANKS!!!...may I have a word with you?  :-)
Date: Wed, 30 Sep 1998 14:47:11 -0500

Bruce A. Frank wrote:

> Has a friend in the Navy named Franks. They were always getting us mixed
> up on the Shore Patrol roster. Lead to some nice nights off the ship
> when the LTJG at the SP wouldn't let me pull the duty because the name
> was wrong on the orders. Anyway....
>
> I have posted my findings and opinions so many times that some might
> want to put ZZZ's on my thread. First off, you do not want or need to
> use anything but mild steel rod for welding 4130 whether it be with
> Oxy/Acet or TIG. The usual filler wire for acetylene welding is E70S-2.
> Dash 3 can be used but it isn't as easy as -2. I like E70S-6 for both
> acetylene and TIG work because it flows well and contains a very high
> level of di-oxidizers to help keep the molten puddle quiet by eating up
> the contaminants.
>
> There are those who use -2D. I tried it and found nothing ro recommend
> it over -6. Some like the "vacuum melt" formulation but at $50+ a pound
> it doesn't offer enough advantage for its high price. Several have said
> that the only thing to use is 4130 filler wire--- an inexperienced
> welder will usually run into problems with 4130 and there are no
> benifits to its use for assembling tube fuselages, landing gear and
> engine mounts. If something in your project needs to be assembled with
> 4130 filler your instructions will say so and that part will likely be
> heat treated after welding.
>
> The last choice is stainless. I have tried all the 300 series and some
> of the 400 series stainless filler rod with TIG on 4130. Again I found
> little advantage over E70S-6 and stainless filler has some
> idiosyncrasies of its own when used on 4130 which in some cases can lead
> to short fatigue life and cracking in the joints.
>
> Mild steel has the "give" needed for the tougher 4130 to move as the
> weld cools and reduces the opportunity for cracks to begin as the
> shrinking filler metal tugs at the toe of the junction between the tube
> and the fillet (that is not a French word).
>
> If you have any more questions, just ask 'em.


Boy I wish I had said that! :-)  I agree though.  70S-6 works great.
It is easy to weld and makes a real pretty weld that you don't have
to apologize for when someone looks closely at the fuselage  you
just finished welding up.  The ONLY reason I would use 4130 rod would
be if the part was to undergo a complicated heat treatment AFTER I
finished the fabrication.  That would not be the case for hardly
and parts in a homebuilt, in any.  The only "heat treatment" we use
as a matter of course is a "normalization" which is kind of like a
tempering process to draw the brittleness while leaving most of the
toughness that we need.

I think I would say in most cases, on a homebuilt, if a part is so
critical and stressed so highly that it requires special heat
treatment after fabrication, it should be redesigned to be less
critical or it will cause endless problems with amateur builders.

From: highflyer <highflyer@alt.net>
Newsgroups: rec.aviation.homebuilt
Subject: Re: Help for a beginning welder
Date: Tue, 15 Dec 1998 09:57:48 -0600

Bruce A. Frank wrote:

> Alan Swanson wrote:
>
> > I am just learning to weld, with the intention of welding the landing
> > gear and other metal parts on a Pietenpol.
> >
> > To practice, I am running beads on 16 ga steel, with Oxweld 32CMS rod,
> > oxy-acetylene.  When I add the rod, I get showers of fine sparks much
> > like you get from a grinding wheel.  The rod is new, and I cleaned it
> > carefully with acetone before using.
> >
> > What am I doing wrong?


You got some really good answers.  I will try to summarize the
important ones.

1.  Set pressures for both Acetylene and Oxygen to around 5 psig
    or a little less.  You can usually read such pressures easily
    on the acetylene regulator.  You may NOT be able to read the
    oxygen regulator easily at those pressures.  If not, set the
    acetylene pressure just under 5 psig.  Then crank the oxygen
    pressure down until you get NO oxygen.  Light the torch and
    open the red valve as far as you can without the flame blowing
    away from the tip and going out.  Then open the green valve
    halfway.  Start turning up the oxygen regulator until the
    orange in the flame disappears and you see a hard blue cone
    in the middle.  If the red valve is not all the way open,
    you can now open it some more.  If you get a "soft" feather
    on the cone, turn up the oxygen pressure a bit more.
    When the  red valve is open as far as you can get it and
    the oxygen valve is half way open and you just barely get
    the "cone" in the flame, then the regulators are set for
    welding.

2.  Filler rod.  The best rod for a beginner to use when welding
    4130 is an E70S-6 rod.  This rod is slightly more expensive,
    but is much easier to weld with because it helps keep the
    puddle quiet.  The key to all welding is controlling the
    little puddle of molten metal.

3.  Tip to use.  The flame, when it is adjusted should make a
    relatively quiet roaring sound.  If the roaring gets hard
    or suddenly increases in volume, you have the gas valve too
    far open.  Close the oxygen, then close the acetylene down
    a little and readjust the flame until the feather just goes
    away.  If it takes more than fifteen or twenty seconds to
    get the puddle started with the flame just starting to get
    noisy, go to the next size larger tip.  If it melts a puddle
    in much less than ten seconds, go to the next size smaller
    tip.  That range gives you the best control over the puddle.

4.  Flame adjustment.  The perfect flame for welding 4130 or
    mild steel is one where there is exactly enough oxygen to
    burn all of the acetylene and NONE left over.  Excess oxygen
    will quickly corrode the hot molten iron in the puddle.
    The iron oxide will spark and jump out of the puddle.  If
    it doesn't get out of the puddle it will weaken the weld.
    Excess acetylene will leave carbon in the molten puddle.
    This will harden the steel where it was melted and make it
    excessively brittle.  This will cause the weld to fail in
    service.  If you are welding stainless steel use the same
    welding rod, but after you adjust your flame, tweak the
    acetylene valve just enough to you barely start to see a
    little feather at the tip of the cone.  This is a "reducing"
    flame and works better for stainless.  Tweaking the gas
    a little to far DOWN so that the feather disappears and
    then a little more, gives you an oxidizing flame and will
    ruin your welds.  You can see it because the cone get harder
    edged and starts to shrink a little.  What you want is a
    relatively long soft blue inner cone right on the tip with
    the edges just on the verge of starting the feather.  That
    is the best welding flame.

5.  Testing your work.  The old pipefitters test is a good one.
    Take a short length of the largest tubing  you can find.
    Cut four pieces that are mitered to the center.  You can
    do that by taking a piece of tubing about an eighth of an
    inch longer than its diameter and then cutting it diagonally
    to get six pieces of tubing with two forty five degree cuts.
    Now you have two saddles and two HALF saddles.  Arrange these
    pieces to make a funky looking ball.  Drill an eighth inch
    diameter hole in the center of one of the full saddles.  You
    have to drill the hole BEFORE you start welding.

    Now weld these pieces together into a ball.  Enlarge the
    hole and screw a fitting into it that will accept a tire
    valve.  Pressureize your ball to about 30 psig and dunk it
    in a bucket of water.  If you see bubbles, you flunk your
    pipefitters test.

    Now comes the HARD part of the test.  Without messing up the
    air fitting, put the ball in the vise and flatten it as flat
    as you can.  Then pressurize it again to 30 psig and put it
    back into that bucket of water.  If you don't see any bubbles
    then, you passed the test!

    Even when you flatten the joint in a vise, it should not break
    either in the weld or next to it.

When you can pass this test easily and automatically, then you are
an aircraft welder! :-)

HF

From: highflyer <highflyer@alt.net>
Newsgroups: rec.aviation.homebuilt
Subject: Re: Brazing 4130 ??
Date: Tue, 08 Dec 1998 10:08:01 -0600

Mike Maddeford wrote:

> I have been emailing back and forth with a fellow who has built a WWI AC.  He
> told me that he used 4130 tube and mild steel plate for all the fittings.
> In the plans alot of parts where brazed, mild steel tube to mild steel plate.
> He went ahead and brazed 4130 to the mild steel.  Is this OK?


I wouldn't recommend it.  Mild steel brazes extremely well and the
resulting joint can be almost as strong as a weld.

4130 Steel is a high carbon steel with a much different grain
structure.  4130 tends to soak up brass into interstices in the
crystal structure and then split when the brass cools.  Brazes
in 4130 tend to be much weaker than in mild steel and cause cracking
problems in the 4130 thin wall tubing.

I believe that there is a mention about this topic in Richard Finch's
"Performance Welding" book also.

HF