# Arc Wander and Magnetic Fields



## Uglydog (Jun 5, 2013)

In a prior thread Rbeckett accurately stated "I use them carefully because they will cause arc wander if you attempt to weld to close to them."

Does anyone on this forum understand physics, electricity, and magnetic fields well enough understand the phenomena? 
If so, can it be simplified so that I can understand it? 
I'm really looking for the why.

Thank you for your patience with us curious types.

Thank you,


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## sniggler (Jun 5, 2013)

The simple answer is the electrons wants to take the shortest route from the electrode to the work clamp (ground clamp), or from the work clamp to the electrode and the magnets confuse the flow enough to cause the flow to be annoyed. Place the ground clamp closer to the weld zone and the magnetic clamp.


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## Ray C (Jun 5, 2013)

It's the same thing as how the old television sets worked.  There was an electron gun shooting electrons from the back of the screen to the phosphor on front.  On all four sides of the tube, there were magnets which were electronically controlled to deflect the beam of electrons causing them to hit the front of the screen in purposeful and predictable ways.  When the electrons hit the phosphor, they released their energy and caused the phosphor to glow.  By manipulating the magnetic filed, images could be presented.

The point being, when a flow of electrons is acted upon by magnetic forces, it alters their path (in the case of the old TVs, the method of altering was precise and predictable).

The formula is R = Mv/qB.  Translated:     Radius of deflection = Mass of Electron x Velocity of electron / Charge of electron x Magnetic Strength.

Does that scratch the itch?

EDIT:  This is how mass spectrometers work.  Every type of atom has characteristic numbers of electrons in the valence orbits; and thus, similar atoms will be acted upon by a fixed magnetic field in the same way.  If a variety of atoms are introduced to a fixed mag field, atoms of a similar type will all be deflected to the same place and will release their engery upon impact.  The apparatus has a target plate, subdivided into many areas -each area is the target for a specific type of atom.  As energy is registered in the sectors, it is then known what type of atom is striking.  This is precisely how Geiger counters work too.  -Very old technology.

EDIT EDIT:  And this is how super colliders detect all the particles that come flying apart when atoms are smashed together.  At the point of impact, they setup a magnetic field and particles are forced to fly into target areas.  They read the engery in the target areas and make estimates about what in the world is hitting in those spots.

Ray


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## MikeWi (Jun 5, 2013)

And to expand on that, when you weld, you're passing electrical current through the work via the arc and that creates an electromagnetic field so...  welding in a corner means the field is unpredictable, causing the arc to wander.


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## Ray C (Jun 5, 2013)

The difficulties with corner welding...  Couple things going on and it depends if it's AC or DC.  DC currents are only capable of establishing electric fields whereas AC currents produce both an electric and magnetic field (with a proportion of about 80% electric, with a quadrature sinusoidal collapse pattern).  The self created magnetic field from AC welding is innumerably small and has no measurable effect on the electrons path.  A fixed magnet such as a clamping magnet is hundreds of millions of times stronger than the self induced mag field.

Common to both AC and DC welding are two phenomenon.  1) Current always finds the shortest path of least resistance.  2)  Sometimes it takes a moment for the current to find the shortest path (due to linear momentum).  Suffice it to say, when the electrode is near two edges, the electrons are trying to figure-out which way to go and they bounce around a little.  Also, shortest path does not necessarily mean shortest linear distance.  If there is scale etc, even a more distant path might have less resistance so, the electrons decide to go that route instead.  ADDENDUM:  Heat effects resistance.  As heat increases, so does electrical resistance (ask me and I'll tell you why)...  On an area of a weld that is really, really hot, you might find the arc jumping to somewhere else even though the electrode is closer.  This is because the localized resistance is so great, the current takes a longer path but of least resistance.

Ray

EDIT:  If you've ever received a little electric shock, you're probably familiar with first a sensation throughout your body then finally, a sudden sting on one localized area such as your hand etc.  There are two reasons for this.  1)  Capacitive discharge:  Your body has many free electrons and they all start to move around when the current enters your body.  This is that overall tingling sensation.  2) They figured-out the shortest path and are now traveling enmasse through one area and it's burning the hell out of some cells in your body.

EDIT (again):  Someone will probably take exception to DC currents only producing electric fields.  There are two distinct cases.  1)  DC current traveling in a wire can indeed produce a magnetic filed.  2)  We're not talking about the case of #1.  We're talking about the case when an open gap has non alternating voltages at the terminals.  This is a very different case and is effectively a capacitor where either air or the electron plasma itself is the dialectric.  In this case, there is, can only be, an electric field.  If you want to know the proof, let me know but, you will need several years knowledge of advanced algebra, calculus and matrix(vector calculus) theory.  -Which are the fundamentals of Maxwell's equations.


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## sniggler (Jun 6, 2013)

MikeWi said:


> And to expand on that, when you weld, you're passing electrical current through the work via the arc and that creates an electromagnetic field so...  welding in a corner means the field is unpredictable, causing the arc to wander.


Mike
I love that observation. Welding from the edge of the flange into the web of a column always causes this issue. It is one of those frustrating things the disruption of the weld puddle make me stay in the corner too long try to keep the puddle together which leads to a excess of liquid flux which causes more issues. To overcome this i try to weld from the middle of the web to the corner and out to the edge or the flange usually it works better, also that inside corner is a bear to clean as well. In the field bringing the ground cable right to the work is sometimes a big hassel but it is always a good place to start. 

Ray, i love when theory meets field conditions, welding in the rain is a bummer 

Tip 1. Lay out the electrodes on a piece of wood and pick them up with stinger instead of the the wet glove. 

*Tip 2. Sit on a wet beam to make weld and put a rod in with a wet glove and the shortest path for the electrons is through the jewel bag it will cure you of welding in the rain.
*
Bob


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## Uglydog (Jun 6, 2013)

RayC,
Have you considered writing for AWS? 
Your stuff makes sense!

Thank you,


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## Ray C (Jun 6, 2013)

What's AWS?

No need for me to write about it.  It was already written by Georg Ohm, Alessandro Volta, James Maxwell, Michael Faraday, Heinrich Hertz and the other contemporaries of the era who figured-out what electricity is.  Written by me is nothing more than a history lesson -and now you know why those electrical terms are capitalized -because they are abbreviations for a proper noun.

Ray




Uglydog said:


> RayC,
> Have you considered writing for AWS?
> Your stuff makes sense!
> 
> Thank you,


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## MikeWi (Jun 6, 2013)

I'm starting to get the idea that this RayC guy is kinda smart.:think1:


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## JohnAspinall (Jun 6, 2013)

Ray C said:


> Someone will probably take exception to DC currents only producing electric fields.  There are two distinct cases.  1)  DC current traveling in a wire can indeed produce a magnetic filed.  2)  We're not talking about the case of #1.  We're talking about the case when an open gap has non alternating voltages at the terminals.  This is a very different case and is effectively a capacitor where either air or the electron plasma itself is the dialectric.  In this case, there is, can only be, an electric field.  If you want to know the proof, let me know but, you will need several years knowledge of advanced algebra, calculus and matrix(vector calculus) theory.  -Which are the fundamentals of Maxwell's equations.



I'm going to disagree with you on this part (and this part alone).  A current produces a magnetic field, period.  There's nothing in Maxwell about current in a wire being different from current in an arc (plasma).  It's right there in the equation that has curl B (B is the magnetic field), and J (J is the current density).  http://en.wikipedia.org/wiki/Maxwell's_equations


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## Ray C (Jun 6, 2013)

In theory, agreed.  In reality, calculate the magnitudes.  Yes, a DC current in a wire produces a magnetic field -a very weak one which is why you need to wrap a wire thousands of times around a ferrous core before you get an effective electro magnet  (right-hand rule:  i.e: the mag fields are additive).  The amount of magnetic field in an open-gap circuit?  Something tells me if you calculated the relative strength of the electric vs magnetic fields under those circumstances, you'd see a negative double-digit number in the exponent.  The context here was addressing another poster's comment that self induced mag fields were causing the plasma to wiggle.  In this case, the electric field is driving the plasma insanely in one direction and the influence of the mag field is about as close to zero as you can get.




JohnAspinall said:


> I'm going to disagree with you on this part (and this part alone). A current produces a magnetic field, period. There's nothing in Maxwell about current in a wire being different from current in an arc (plasma). It's right there in the equation that has curl B (B is the magnetic field), and J (J is the current density). http://en.wikipedia.org/wiki/Maxwell's_equations


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## JohnAspinall (Jun 6, 2013)

I suspect we're 99% in agreement, and simply disagreeing about what comparison we're making.

I was not comparing electric field to magnetic field.  I was comparing magnetic field from current in arc, to magnetic field from current in wire.
The magnetic field from 1 Amp in an arc is the same as the magnetic field from 1 Amp in a wire.  (Assuming the geometry is the same, etc., etc.)

As for wiggle, we agree.  The effect of magnetic field from arc current is tiny.  The dominant factor is multiple equally-preferable arc paths leading to different parts of the workpiece.


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## Ray C (Jun 6, 2013)

We're both wrong!

The wiggle depends on how many cups of coffee were consumed prior to arc welding and if a bee has suddenly decided to seek shelter from the bright lights and hang-out with you behind the welding mask.  -Silly...  How come we didn't think of that before?


Ray




JohnAspinall said:


> I suspect we're 99% in agreement, and simply disagreeing about what comparison we're making.
> 
> I was not comparing electric field to magnetic field. I was comparing magnetic field from current in arc, to magnetic field from current in wire.
> The magnetic field from 1 Amp in an arc is the same as the magnetic field from 1 Amp in a wire. (Assuming the geometry is the same, etc., etc.)
> ...


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## Shade (Jun 6, 2013)

Ray C said:


> EDIT (again):  Someone will probably take exception to DC currents only producing electric fields.  There are two distinct cases.  1)  DC current traveling in a wire can indeed produce a magnetic filed.  2)  We're not talking about the case of #1.  We're talking about the case when an open gap has non alternating voltages at the terminals.  This is a very different case and is effectively a capacitor where either air or the electron plasma itself is the dialectric.  In this case, there is, can only be, an electric field.  If you want to know the proof, let me know but, you will need several years knowledge of advanced algebra, calculus and matrix(vector calculus) theory.  -Which are the fundamentals of Maxwell's equations.


I would love to see the proof.  I have taken Multivariate and Vector Calculus, Differential Equations, Numerical Methods and 2 semesters of Quantum Mechanics, do I qualify.  I also want to see how plasma is a di-electric.


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## Tony Wells (Jun 6, 2013)

This is all well and good, but you cannot limit this effect to the fields around the arc itself. There are almost infinite variables involved in the position of the arc in relation to all the cabling and the material being welded. Whether there is a mag field around the arc or not, it is likely more the interplay of the fields generated by the current passing through the materials than the arc itself since they are a ferric conductor. Definitely agreeing with John.

And yes, I understand the math, etc, etc.


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## Uglydog (Jun 6, 2013)

Ray C said:


> What's AWS?
> 
> No need for me to write about it.  It was already written by Georg Ohm, Alessandro Volta, James Maxwell, Michael Faraday, Heinrich Hertz and the other contemporaries of the era who figured-out what electricity is.  Written by me is nothing more than a history lesson -and now you know why those electrical terms are capitalized -because they are abbreviations for a proper noun.
> 
> Ray



AWS = American welding society.
I want to be careful to not offend any AWS writers and their ilk, as they put out a decent magazine and work hard to improve quality within the industry. 
However, I wish they would spend a little more time on theory. Instead of merely application.


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## Uglydog (Jun 6, 2013)

Tony Wells said:


> This is all well and good, but you cannot limit this effect to the fields around the arc itself. There are almost infinite variables involved in the position of the arc in relation to all the cabling and the material being welded. Whether there is a mag field around the arc or not, it is likely more the interplay of the fields generated by the current passing through the materials than the arc itself since they are a ferric conductor. Definitely agreeing with John.
> 
> And yes, I understand the math, etc, etc.




While all of this quit making any sense several posts ago, it has been very helpful.
It might be interesting to track how many views this theory stuff gets.

Wonder if once a month (week?) it would make sense for someone to systematically ask a strictly theory question which has obvious practical application for the masses and see if members respond with a goal of the gurus having fun gently poking each other, and occasionally making sense to the rest of us.

If it were me, I'd probably start with Machinery's Handbook as it's on most members shelf regardless of their penchant.


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## Tony Wells (Jun 6, 2013)

Good idea, UD. I know a lot of it might bore some, and it's not alway applicable to hobby machining, but I'm sure there would be some interest. After all, everything that goes on in the shop has theory behind it, and is simply a manifestation of the theory, put to work.  A discussion that allowed people to make the mental connections between theory and practice could be very valuable.


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## Terrywerm (Jun 6, 2013)

Despite all of the great responses, I have to state my appreciation for sniggler's first response - the part about the current being annoyed.  You just CAN'T make this stuff up, can you??   :roflmao:


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## Ray C (Jun 6, 2013)

Well, it might actually be right...  Magnets probably (almost certainly) cause some local polarity alignment in the steel and when the little electrons see an army of aligned atoms they stop and wonder for a while if they're courageous enough to pass the resulting field...  Then again, the field could be pulling them in even though there's a closer escape path and they initially decided to go there instead.  Quite a decision for the little fellows to make...

Here's a quick different "theoretical question"...  On many occasions, I've had a glob of weld that always attracts the arc even though I've cleaned the daylights out of the surrounding area, cleaned the tip of the electrode and I'm holding the rod closer to the area I want to build-up.  Now we all know this is the perfect setup to weld-in an inclusion but, for some things, you just don't care.   Really wonder why this happens this way...



Oh, and BTW, on the problem of magnetic field strength from a couple posts ago, I'm assuming 25V OC and 100Amps.  Once I calculate the strengths of the fields, I'll think-up a way to relate how much work each field is capable of.

Ray





terrywerm said:


> Despite all of the great responses, I have to state my appreciation for sniggler's first response - the part about the current being annoyed.  You just CAN'T make this stuff up, can you??   :roflmao:


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## Rbeckett (Jun 7, 2013)

This is a great thread!!!  The theoretical discussion is even interesting as well.  In welding however the arc wander is just a source of irritation that must be minimized to prevent slag inclussions and imperfect weld zone.  A wandering arc causes localized heat affected zones that cause Martensite formation and Helium inclusion in the base metal.  These two formations negatively afeect the quality and strength of the weld at a molecular level.  If you are welding and notice that the arc is wandering (and you will notice), you need to either move your ground or move your magnetic squares further away from the weld.  Once you have experienced the arc wandering you will begin to notice about how close you can get before it begins happening again.  Best practices dictate that once jigged and properly tacked mechanical means of retaining the joints designed angularity is better than a magnetic means every time.  That is why I frequently weld my jigging fixture to the surface of the welding table and only remove the jig after the completed weldment has been allowed to cool and been removed. It makes setting a repeatable and uniform spacing in a quick and easy no hassle way. This will increase through put and fatten the wallet.  The result that we are all looking for ultimately.  Great discussion!!!
Bob


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## SE18 (Jun 7, 2013)

so far you're referring to AC or DC welding. Using OxyAcy won't cause arc wander b/c there's no arc, correct? And heat itself won't destroy the magnet, right? For instance I think the sun has a magnetic field and that gets pretty hot.

The only thing that would cause a magnet to lose its magnetic field is dropping it or slamming it hard with something.

I'm not sure how a demagnetizer does the work of demagnetizing things.


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## sniggler (Jun 7, 2013)

Even if i cut up a little here i really like this thread usually at work ironworker/welder im the one trying to bring in welding theory to the discussion and i just get just weld it. Trying to understand what's really happening helps inform me as to the possible solutions and that makes this thread very useful. 

Welding programs often teach to the test in the booth and the theory is just a forgotten power point or video. That reminds me one of my last supers ran off with my Lincoln Procedure Handbook of Arc Welding:angry: i brought into settle the old deeper or better polarity and penetration relationship argument, great book but nobody conceded.

Bob


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## Shade (Jun 7, 2013)

SE18 said:


> so far you're referring to AC or DC welding. Using OxyAcy won't cause arc wander b/c there's no arc, correct? And heat itself won't destroy the magnet, right? For instance I think the sun has a magnetic field and that gets pretty hot.
> 
> The only thing that would cause a magnet to lose its magnetic field is dropping it or slamming it hard with something.
> 
> I'm not sure how a demagnetizer does the work of demagnetizing things.


Actually heat can effect a magnet but you have to get them quite hot.  In a magnet the grains or crystals are aligned in the same magnetic direction.  If you heat them up enough they can reorganize and then when they cool they will either be weaker or potentially loose their collective magnetism.  For example nickel becomes, non-magnetic at 631K (676F) if a lump of nickel was heated to 676F or higher and then allowed to cool in a strong magnetic field it would gain some permanent magnetism, we did it to 1600F because that is the temp our muffle furnace was set to, bored geeks at work.  Maintenance was ****** we use all their copper wire for the electromagnet.  We used the 50 gram nickel balls for the GM-Quenchometer tester.  To demagnetize them all we did was run them through the furnace again and cooled the outside the magnetic field.  http://en.wikipedia.org/wiki/Curie_temperature


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## Ray C (Jun 7, 2013)

The temperature at which a metal becomes non-magnetic is called the Curie point and very closely aligns with the "critical temperature" which, in heat treating is the temperature when the metal becomes Austentite (i.e. fully considered a solution). Most old-fashioned heat treating techniques called for heating until a magnet wouldn't stick -then give it a little more heat (crude and sometimes effective).

The formula for Kelvin to Fahrenheit is: F = 1.8 x (K - 273.15 ) + 32.


Typical temperature for steel is around 1475 to 1550 F. Pure elements such as nickle have much lower Curie points.

BTW: The Curie we're talking about is Pierre Curie -not Marie Curie.

Ray

EDIT: And by the way, Austentite is named after William Roberts Austen (late 1800's). Curie and Austen were contemporaries. And by the way, I will bore everoyone with these history lessons of "who and when" as I feel it's fundamental knowledge -just as important as the techniques we employ because of their genius contributions.


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## SE18 (Jun 7, 2013)

magnetic fields in the sun seem to violate that curie principle

http://en.wikipedia.org/wiki/Stellar_magnetic_field

this seems to be another one of those mysteries.

(not related to this but the biggest science mystery I could never find the answer to is they say pollution causes the greenhouse effect and global warming. Yet, if a massive volcano spews pollution on a global scale, that causes global cooling)


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## JohnAspinall (Jun 7, 2013)

SE18 said:


> magnetic fields in the sun seem to violate that curie principle
> 
> http://en.wikipedia.org/wiki/Stellar_magnetic_field
> 
> this seems to be another one of those mysteries.



No mystery, no violation.  The Curie point is where *ferromagnetic metals* lose their magnetism.  The Sun is not metal.  

The Sun is plasma ( http://en.wikipedia.org/wiki/Plasma_(physics) ), like the welding arc that started this discussion.  Plasmas conduct currents really really well, because plasmas are made of charged particles.  When charged particles move (more precisely, when the positives move differently from the negatives) that* is* a current.


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## SE18 (Jun 7, 2013)

the earth's core is hot iron (supposedly), but earth has magnetic field?


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## Ray C (Jun 7, 2013)

Yep...  Now don't quote or nitpick me here but, the Earth is something like 85% metal.  Indeed, much of the core is beyond the Curie temperature but molten metals can still carry electrical currents.  As magnetic waves fluctuate from the Sun and go past the Earth, it induces currents in the molten underlayers and those currents in-turn, produce a magnetic field of their own.




SE18 said:


> the earth's core is hot iron (supposedly), but earth has magnetic field?


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## JohnAspinall (Jun 7, 2013)

*General Curiosity *[was: Arc Wander and Magnetic Fields]*

I'm going to respond to SE18's (great) question about the Earth's magnetic field, but first I wanted to say something more general.

I'm really really delighted that people are asking these kind of questions.  It strikes me that quite a few of these questions would be covered in an introductory materials science course.
When I did my engineering degree (cough, choke, almost 40 years ago), every engineer (no matter what specialty - mechanical to chemical to electrical) had to do a "Materials Science for Engineers"
 course, and that was one of the most enjoyable courses I took.  Judging from a quickie search, many, if not most, programs have a similar requirement today.

My suggestion for many people is: go find what text book your local college uses for this course.  Don't buy it new (new textbook prices are insane), but grab up a used copy.  Or get an old edition.
Or find someplace doing a MOOC ( http://en.wikipedia.org/wiki/Massive_open_online_course ) and find out their course materials.  
Look through some Amazon suggestions like http://www.amazon.com/Materials-Science-Engineering-An-Introduction/dp/0470419970/ .   (Disclaimer, I haven't read that one, it just popped up first on my search.)
Get curious!


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## Ray C (Jun 7, 2013)

*Re: General Curiosity *[was: Arc Wander and Magnetic Fields]*

That's very good advice, John.  Good idea there.

-And you'd be surprised the amount of basic stuff no longer taught in modern curriculums.  We have summer interns once in a while and it blows my mind how much things have changed in many schools.  Top Tens are still doing a good job of teaching the basics but, your basic State colleges are just pumping kids out.  In so many ways, the'ye turning engineers into technicians as they only know the superficial "how" -and not fundamental "why".  Basic problem-solving abilities have plummeted!  I've even seen a trend where graduate student studies are teaching "true fundamentals" as they were once taught as the beginning courses which preceeded all others.  I guess it's a different way of going full circle.

My latest trick is to hire mainly physics students to do EE work.  Mechanical Engineering curriculums still seem pretty good though...







JohnAspinall said:


> I'm going to respond to SE18's (great) question about the Earth's magnetic field, but first I wanted to say something more general.
> 
> I'm really really delighted that people are asking these kind of questions. It strikes me that quite a few of these questions would be covered in an introductory materials science course.
> When I did my engineering degree (cough, choke, almost 40 years ago), every engineer (no matter what specialty - mechanical to chemical to electrical) had to do a "Materials Science for Engineers"
> ...


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## Rbeckett (Jun 7, 2013)

Sniggler.
The Lincoln Foundation book is truly the Bible when it comes to arc welding and theory.  That book coupled with the Miller Student resource package and a concerted effort to practice proper welds is really all a welder needs.  Back when I started out that was not even mentioned as a source of info.  All I got was the "because that is how we always do it. I don't know why, I just do it" answers when I asked why things were done a certain way.  After I availed myself of the knowledge that is made readily available to any one who is interested enough to ask, my welds and their performance became much better and 100% more consistent.  I generally can run a perfect bead 96-97% of the time, and know when it is time to grind out a screw up and do it right.  I am not a technically trained or schooled welder, but would venture to say I can hold my own with just about any one of them and not have failed welds.  I may not be able to accurately explain everything exactly like the book, but I know where to find the answer if I am unsure or don't know already.  So if you don't have those two sets of literature, spend the few bucks and learn a ton just for the price of admission.  It's cheaper than One Day at Disney or Busch Gardens and can change your life if you let it.

Bob


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## Alan Douglas (Jun 7, 2013)

> I've even seen a trend where graduate student studies are teaching "true fundamentals" as they were once taught as the beginning courses which preceded all others. I guess it's a different way of going full circle.


Not necessarily a bad thing.  Fundamentals may not make much sense until you've had some practical experience.  The kids who have experimented and built things before college may get it, while the ones who spent their time with video games may not.  I had EE classmates who couldn't solder (but they could run rings around me in math).  I spent three summers in a motor repair shop, so the electric machinery course was a breeze; some classmates had no idea what they were doing.


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