Kevin, I know in the past you have said that you only post heat certain joints of your fuselages. Well I'm at the point of considering doing so also. I assume I want to do it before adding the side and belly formers etc or do you wait until just before powder coating? Can you tell me which joints I should do, and a basic step by step on how? - Darin
Darin, post heat is a tricky thing to do correctly without damaging the 4130. We use a rosebud for all heating of 4130 tube, sheet as well as alum that we anneal. Ours is about 1/2" dia tip on it.

Your assumption that this is done prior to formers etc is correct. Chances are you have already done it on your airplane. Did you heat the lower longeron and flying wire lugs when forming the lug in place? How about the front and rear lower wing attach fittings and the cabane lugs? That is what we do. Heat the area a bit when forming those, then finish welding those fittings with no added heat afterward. KK
I'm not sure if I accomplished any stress relief when forming the fittings. I was careful to heat only the sheet metal as much as possible for forming and was only using a welding tip. I do know those joints sure got heated up when I was welding the fittings on. So I guess the question is should I go over them again with a rosebud?

If I understand correctly you do not post heat any clusters other than the ones that get heated when forming the fittings to them? Sorry if I'm not up to speed on this, if I remember right, Richard Finch in his book advocates no stress relieving, while other sources say to do all joints. - Darin
Darin, do no additional heating at this point. Leave well enough alone. We do not post heat the fittings after forming and welding them on.

Post heat is a correct way to refer to this operation. Torch normalizing is correct as well. Stress relieving is NOT a correct term.

Post heat: apply heat after joint welded.

Torch normalize: warm the 4130 to dull red, remove heat and let cool slowly in very still air to return the metal to Cond N status. This can be done to increase the strength of 4130 cond A to make it cond N as well as bring cond N 4130 that has been welded and hardened back down to cond N 95,000PSI.

Stress Relieve: To do this, the entire part needs to be heated to a dull red all at one time in a large enough oven to hold the part and then let cool in still air. The part should be jigged in a very substantial fixture that is not affected by heat such that the part does not change shape if the part has fitting holes etc in it. Typically, if a part is to be stress relieved in manufacturing, it is built but has not had attach points final machined and drilled, then stress relieved, cooled and then jigged in a final fixture for spot facing and drilling of the attach holes, fittings etc.

Annealing 4130 can be done with a torch as well. This will take 4130 cond N 95,000PSI and reduce it to cond A of around 45-55,000PSI. This is useful for forming of parts. After forming, normalize to cond N. The reason I bring this up is that applying the heat wrong can result in a weaker structure.

Torch normalizing locally heats the part and in many cases, affects the alignment. Spiral welding minimizes the stress introduced during the welding process. Heating the structure at one joint can result in all stresses in the frame to be concentrated at that joint resulting in a bulge in the tube at that point. This will affect the frame dimensions and as you know, a bulge must be patched. If you patch it, you weld it again, etc.

All factory built Pitts and Husky airframes have been TIG welded since the 1960s. Maule frames are MIG welded. Most factory welded parts use arc welding of one form or another to assemble weldments. In the case of Maule and Pitts, there is not stress reliving or torch normalizing done. Basically, it is a "bird in the hand....." sort of thing (no pun intended in ref. to Finch) KK


I took a look in my copy of "Aircraft Tubing Data" by Summerill Tubing Co. for details on cleaning and protecting steel 4130 tubing. This book is the bible on strengths, manufacture, testing etc of 4130 tube sructures in airplanes. In the Corrosion Protection section, reference is made to the accepted manufacturing processes used in airplane parts.

To quote the author of this section, Woodrow, "In the instance of tubular structures, the tubing must be thoroughly protected against corrosion following the cleaning prior to the burning off of the original preservative during welding, heat treating and sandblasting."

From this single statement, we can learn that the guys who invented the tubing we use in our airplanes expect the user to wipe off the oil, burn off what is left during welding, heat treat it if needed, and then sandblast it. Later in the section they go on to discuss primers and paint.

So wiping off the oil and cooking a bit of it off near the weld is all that is expected when welding 4130 tubing. They do mention protecting the areas that got burned completely free of oil. So, based on this reference book, polishing the tube may be better than not but not to a degree that makes it worth the effort.

Sandblasting is also fine and accepted as the normal way of cleaning 4130 tube as long as it is not done with extreme force deforming the material being cleaned. Sand or bead blasting should be done prior to heat treatment so that all the scale is gone prior to HT for even heat penetration. So again, the guys who invented this stuff think the losses by sand or beadblasting are not great enough to be a negative.

We wipe the oil off, weld it, coat the weld areas post weld after cooled, sandblast, powdercoat.

All this concern of sandblasting and cleaning to bright metal may just be "careful bisection of human cranial moss", (splitting hairs). Heat it up and form it with a "Portable Handheld Inertial Driving Unit." If that doesn't work, get a bigger hammer and hit it again! KK


Steve, I looked at your weld samples and you can assume from my response that you are good to go. The welds were very nice with good penetration, color, heat, etc. They are on the small end of the acceptable bead width and if you feel you want a wider bead, feel free to do so. The beads we produce are typically 3/16" wide. For the most parts, the tubes you are welding together are .035 or 049 thick. IF your weld beads are such that they are double that plus 20%, you are there. The exception on the model 12 would be the front longeron points and other heavy wall tubes. There you need to have greater penetration and bead size. For example, the engine mount bungs, -77, and the 1.25"dia sleeves require about a 1/4" bead on them.

Refering to your added questions:

1. I know the literature typically suggests .040 tungsten for most of the work done in building a tube frame airplane. However, other things come into play. We use 1/16" for everything except the heaviest of alum welding I do. .040 is too tiny and you end up breaking it off with the slightest tap of the tip to a tube as you try to get into position. The small stuff burns off at the tip too fast too. Stick with 1/16 2% thorated.

2. You can use acetone to clean the tubes. A stainless steel wire wheel will clean the tubes in the weld area. Just clean in the weld area and leave the coatings on the tubes elsewhere. Some fine sand paper will work as well. I am sure the hangar has a few folks that can make additional recommendations on how to clean the tubes for welding.

3. We do NOT preheat the bungs. Just pour on the amps. KK


An 1/8th of an inch when fitting tubes... REALLY? on each end? I knew that you were supposed to have a gap but was thinking in the neighborhood of 1/16th at each end. Gordon
Amateur fun with numbers. A few assumptions. Steel is liquid at about 2600F above room temperature. It's coefficient of thermal expansion/contraction is about 0.000006" per inch per degree F. The weld bead, ie the section that is actually added to the part in the liquid state, is about 1/4" wide. Assume no outside forces or constraints, just thermal contraction of the weld bead. If we assume the entire bead is kept in the liquid state as we weld, then the assembly will shorten .000006 x .25" x 2600, or only .0039" as it cools to room temperature.

The actual shortening is gonna be less because the entire weld bead isn't kept liquid as we move around the tube. It's in a plastic state (red hot), a lower temperature. It has some tensile strength. However low it may be, it's more than the liquid material under the torch. The liquid metal gets stretched as it cools to the plastic state because it's constrained by the already solid metal around it. "Orange" is about 1700 degrees, so the actual contraction of the weld bead is about .0026". Obviously, contraction of the weld bead as it cools doesn't justify 1/8" gaps.

Ok, what about the fact that the whole tube lengthens because it gets warm during the welding process? Just for fun, assume the whole length of a 24 crossmember is raised to the orange-hot level. Linear expansion would be .000006 x 24 x 1700, or 0.2448". Hey, that's two times an 1/8" gap, but perhaps our welder is using a bit more heat than necessary .

In reality the linear expansion of the tube is far less. It's only hot at the ends, and real hot only in the last few inches. If we say the first 8" is a temp gradient from 1700 to 200, then the expansion is something like .040" In any case, it doesn't matter. You fit the tube cold. It gets longer as it warms, then returns to it's original length after it cools. The assembly you welded it into winds up shorter by little more than the contraction of the weld bead, the only component that was added to the picture in the high temperature state.

Ah, you say, the exception is if the expansion was constrained by the structure. Then the expanding tube deforms into the plastic weld bead, and the total contraction becomes the sum of weld bead contraction and tube contraction. Yep, no question, but that has little to do with fitting gap. The gap got fixed into the structure with the very first tack weld; it's a solid bridge across the gap and has the same dimensional effects as a tightly fitted joint. Even if you don't buy that argument, we've already shown that our total expansion/contraction is perhaps .042", which is far less than a .125" fitting gap.

A welded joint could be described as cast metal (disorderly grain structure) connecting two wrought members (orderly grain structure). Increasing the distance bridged by the disorderly grain structure hardly improves the strength of the assembly. Castings are never as strong as the same wrought material. There's also the practical aspect; gas or tig, it's harder to bridge big gaps and get sound welds. Too easy to burn away an edge. Now we're filling holes with cast metal.

So anyway, it looks to me like minimum gaps are best, with very few exceptions. You don't have to make yourself crazy about it. I tend toward the good old rule that says "gaps less than the thickness of the rod". Dan
"The gap got fixed into the structure with the very first tack weld; it's a solid bridge across the gap and has the same dimensional effects as a tightly fitted joint. Even if you don't buy that argument..."

I buy it. I buy it completely. I got a Skybolt fuselage in the shop that buys it too. Too late in the process I discovered I could prevent a lot of distortion if I did the following:
1. Tack weld the tube into position normally like everyone says.
2. Carefully take some appropriate measurements of the area of the fuselage you are about to final weld.
3. Weld up the tube at one end as usual.
4. Take the same measurements again, and if there are any distortions in the area (at the other end of the tube you are now about to final weld) over, say 1/16", 1/32", or whatever seems tolerable to you at that particular location, then
5. Carefully cut the tack welds at the other end of the tube with a reinforced Dremel cut-off wheel,
6. The fuselage then suddenly goes "PRANG" back into position.
7. Re-tack the tube to hold it in place, and then final weld.

BTW, I'm talking about gas welding. I've never picked up a TIG torch, so I can't say about the process with that. This isn't something I would do all the time as it's not necessary, but I can think of 6 or so areas it worked great for me, especially in the many tube clusters at the rear, on the round tubes connecting the square tubes to the streamline tube on the I-struts, and a few other areas I wish to high heaven I had, such as on the bottom forward tubes. I've never heard of anyone doing this, but I sure never had any problems doing it. On the contrary, it helped me a lot, occasionally dramatically.

I'm an engineer by trade and would love my fuselage to measure out perfect, but building this plane has taught me the need for practicality. Welding up that fuselage is easily the most GDMF frustrating thing I have ever done. It turned out ok, but sometimes I wish I had the balls to just chop it up and start all over. I could do a so much better job now. Maybe on that Skyote I keep eyeballing...;) Scott
I'm about 2/3 through the finish welding of my Pitts 12 fuselage, and it doesn't seem to distort much at all. I'm also using the spiral forward from the tail method advocated by Kevin: Pitts12WeldSequence.htm which hopefully will take care of any distortion that is there. About all I've noticed so far is that most of the little thin wall tubes tend to tuck in just a little from being heated only on the inside of the structure. Here's a picture of my lower rear longeron (.75 x .035 tube): TubeTuck.jpg

From what Kevin has said, a little mallet & wood block work later will fix it where it will show. But then I'm using TIG, which doesn't seem to put as much total BTU's into the structure. Plus I tend to weld a bead, then a little time setting up for the next one so I can be comfortable with the torch and rod. I think it lets the heat dissipate some in the fuselage, and my torch too, which is air cooled.

I know what you mean about doing a better job the next time. I'm sure my first welds on the fuselage are solid, but they aren't as nice looking as the ones I'm doing now. I can see the improvement as I move forward on the fuselage. Mostly its the fine coordination of torch and rod that improves with time. I just keep telling myself I'm only building an airplane, not a Steinway piano. As long as its straight and solid, it will fly great. I know all my R/C's did, no matter how ugly they were. Darin
Good job Darin, Making the iso drawing is a good idea. Wish I would of thought of it. Your tube tuck, as you call it, is far less than when you gas weld, however these do look like fairly close and heavy tubes. My Cub had some fairly long stretches between clusters with smaller tubes and the bending was much more pronounced. If the longeron touches the fabric(most do) you need to get that out of there as it will look bad on the finished airplane. Using a gas torch heat the outside of the cluster cherry red hot and let it cool without any air movement in the shop. This will help quite a bit and make the pounding a little less nerve racking. I always thought it was difficult to hit your airplane that hard, but I guess you are just proving how strong it is. If you use a block of wood and a steel hammer I would suggest making a rounded indentation in the wood block to kinda fit the tube size. You don't want to knock any flat spots in your tubes as that would significantly weaken them. That is why I use the rubber hammer. Keenflyer
Thanks for the compliments, but the iso drawing is actually Tom Weinberger's drawing of Kevin's specified weld sequence for the Pitts 12 that I dressed up a bit before putting it on my site.

The tube tuck shown is on the 3/4 - .035 aft longeron tubes. I got out my skybolt plans to compare the tail section. The picture was a view of the bottom right longeron, looking forward from the tail. In the tail, the longerons are 3/4-.035 just like the skybolt, but the spacing is actually about 1" further between clusters than on a skybolt. Repeated link of picture TubeTuck.jpg

Also, I fitted my tubes as tight as reasonably possible. I do find the tight fits are easier to weld, since the edges aren't as prone don't melt away. So...do you just use a rubber hammer without a block, or are you using both? I'm curious since that will probably be my next task. Darin
Darin, No I do not use a wood block as the hammer face is softer than wood. This is an old hammer that I have had for over fifty years. I have no idea where I got it or what it is really for but it sure is nice for pounding hard on things you do not want to damage. I have even straightened auto mag wheels with it and they tell me that you can't do that. It has a medium to hard rubber end that is about three inches in diameter and about three inches long. The other end is steel and a little smaller. I have used it for bumping out oil cans and such on auto bodies and many other things. One thing about this straightening thing. Don't start out with heavy hits. Be gentle and increase the force only as far as is necessary. You definitely do not want to dent the tubes. Keenflyer
We TIG weld all our stuff Model 12 and otherwise. All our parts are fitted with as near zero gap as possible and we have no problems with twist or distortion. I have found that when welding 4130, if you allow room for movement, the tubes will move. If you do not allow movement, they don't move. Fitting the tubes close will keep things straighter no matter what method of welding you use. The 1/16" gap on each end is a typical max not a must have. 1/8" is far too large a gap on both ends.

I have a copy of Aircraft Tubing Data by John E. Younger of the Summerill Tubing Company dated 1943. This is the 'Bible'" for aircraft tube structure material and component design etc. It lists all data on 4130 tube and mild steel tube how to form, it how to cut, it how to design the joint of tubes etc. and HOW TO WELD IT! This text addresses all forms of welding, gas, tig stick, mig etc. even though some of these were quite new at the time this book was compiled. Here are some quotes from the tube structure welding section:

Under the Gas Welding section:

"Spacing: Most welds in aircraft work are fillet welds of one form or another and for this type of weld no spacing is needed............"

"Usually welding warpage can be controlled by the adoption of a set of welding sequence for each assembly."

In the Arc welding section:

"Shop Fabrication of Tubular Structures: All joints of tubular structures to be arc welded must be rather closely fitted IF the full benefit of this process is to be attained. To obtain this type of fit by hand cutting and filing is a slow and expensive (labor time - KK) procedure, but the following methods can be used with speed and economy......."

So, if you go back to the actual info available on 4130 structure design from the time 4130 was being used by most of the aircraft industry (vs. plastic now), tighter is better for tube joints. I think the 1/16" gap stuff came from the EAA publications in the 60s. If you read this text that I have here in the section for plate butt welds over 3/16" thick, they call for 1/32" gap for penetration. It is easy to see how someone could read this and merge it into a discussion of tubes, do the math of 1/32" on each end gets 1/16" overall shortening and then state that a 1/16" gap is good. Then someone else change it a bit to say a 1/16" gap is required on each end to finally someone thinking that 1/16" x2 is 1/8" total length change only to use 1/8" gap on each end. Etc.

I prefer to use the data from the guys who invented 4130 and how to use it to build airplanes. Get a copy of this book and see how many times you will say "Well, I'll be darned". KK

04/01/01 WELDERS

Newbie builder here.  I am looking into getting a small TIG welder.  I have considered the Miller and Lincoln products, but what about Hobart?

I have been looking into the Lincoln Square Wave 175 and the V200-T.  Along with the competitive Miller product.  I just recently saw Hobart's TIGMATE unit.

I see that the 175 Lincoln has a lower amperage range, down to 8 amps (or so) in DC mode.  The Hobart only goes down to 20 amps.  I have had a little gas welding experience, but have no feel for how much current is needed for "typical" aircraft welding.  Any help would be greatly appreciated.   -Phil
I'm a firm lover of Miller welding equipment.  We have 2 syncrowave 250 Miller machines.  One is 10yrs old and the other is about 5 month old.  They weld EXACTLY the same.  I like the consistency and quality of the arc on both alum and steel.

I have tested the Lincoln 175 squarewave, Miller Econotig, Linde 250, Miller 250, Lincoln 275 etc.  The lincoln 175 is the best I have seen for our type of welding in its price range ($1200 and less). The Econotig is not a good choice because the start amperage is too high.  In the 250 amp range, the Miller syncrowave 250 is the BEST of them all.  Miller has a new Tig 180 that is to compete with the Lincoln 175.  Specs have it on par with the 175 and I will test drive it, as will Jeff our other shop welder, and I can let you know how it works.  Jeff and I are gonna try all the Lincoln and Miller models and compare them size for size.

Miller and Hobart are both owned by ITW.  ITW owns just about everything!!!  Go to ITW.com and you can see that not only do they own these 2 welding companies, but both Binks and Devilbis spray equipment, LPS, Dykem, MagnaFlux, and more.  They began a 'streamlining program' sometime back to reduce the number of redundant products in the various brands.  They market welding and cutting mahcines as both Miller and Hobart equipment.  Same stuff, black or blue case.  Liewise in Spray guns.  So, if you look at a Miller 180, you are looking at a Hobart TigMate you are looking at the Miller EconoTig.  150amp max min 20 amp unit.  Not good for thin 4130 work.  I bet that Hobart will have a repainted Miller 180 soon as the 150 amp unit is loosing its luster.

You want as low a start amperage as possible.  Our 250 Millers start at 5amps.  A Miller 351 starts at 3 amps and a Miller Aerowave starts at 1amp. Less than 10amp start is a must for .025 4130 tail ribs or similar work.  Our 5 amp is real sweet!  1amp would be fabulous.  Of course price is the issue here.  8 amp start machine is $1200, 5 amp start is $3500, 3 amp is $4500, 1 amp is $9000.   KK


A Makita battery drill is what we use to sharpen our tungsten.  Place it in the chuck, pull the trigger and lean it against the belt sander.  BTW, the tungsten point will last longer if the sand scratches are parallel to the length of the tungsten rather than perp to it.  To do this, hold the drill off the end of the belt sander with the belt pulling away rather than holding the drill off the side of the sander.  We sharpen 6 or 8 pieces at a time too.  Also, don't sharpen both ends.  That blob you push thru the collet will be real hard to pull out later.  KK


Is the gas lens a better deal?  Also they state it will allow you to have the electrode as much as one inch or more away from the work.  - Charles
Charles,    Gas lenses have been around about as long as the TIG process.  Yes, you do get better gas flow with a lense as compared to a collet body.  Is it needed in most applications we deal with here?  No.  Some yes, all no.  We use a gas lense on some parts, not others.  If it is better, why not always use it?  Because the gas lense and its ceramic cup are much larger in diameter than the collet body and its cup.  If you have tight sopts to get into, a gas lense is not a good tool for that.  ANother negative is cost.  A third is that gas lenses don't last as long as a collet body and get dirty, plug up from spatter etc.

We have both gas lenses and collet bodies in our shop for 2 sizes of torches we use here.  Each job has its own requirements.

I recommend that for the type of welding we do here, you use a #6 cup.  No smaller.  Set argon flow to 15cfm.  Work in a no wind condition.  Tungsten 1/4" to 3/8" out of cup.  A smaller cup creates too much velocity in the gas and the gas bounces off the weldment.  KK


I just watched some of Richard Finch welding video and as to stress relieving he doesn't buy it. Says try it yourself, weld up a square frame then cut one side of the frame in the middle. Any stress within the frame will be seen at the cut by offset in the tubes. Unless you use a oven you're wasting gas and changing the steel hardness #'s. Oh, he also pushes Sharpie pens. Denis
Let's chat about stess relieving. There are a few terms that get tossed around with this subject.  Stress Relieve, Normalize, Anneal. Normalized is the condition the 4130 tube and sheet comes in noted on the material as Cond N and has a tensile strength of 95,000PSI.  Cond A or annealed 4130 has a tensile strength of around 50,000PSI and us used to make parts that are stamped etc. and later is changed to Cond N by being subjected to a normalizing process in a heat treat oven.  

Stress Relieve is a term that applies to relaxing a structure that has alot of stored energy in it.  For example, you weld up a frame and later cut it apart in one spot.  It springs closed or open with a great "boing".  That frame had stored stresses in it that could have been caused by misalignment, excess material shrinkage during welding etc.  Typically, when stress relieving a frame, you will get small bulges or slight neck downs in the tube near a joint. This is the internal stress in the frame moving the metal that is softened when heated with the torch.  What is bad about this?  The buldge or neck down of the tube is enough to require a repair of that spot.  In certified airplanes, race cars parts etc., an exposed bulge or neck down is considered a flaw that needs a repair.  Secondly, if your frame was straight before the torch stress relieve process,chances are it won't be after unless it is in a Class A jig that holds it exactly where it is supposed to be.   Stress Relieving requires the metal to be hot enough to become soft like if you are bending it.

Anneal is a term that refers to having the metal in its softened state.  This, as I touched on above, aids in forming the metal.  We do this to form alum instrument panels, etc.  Some metals will stay at this annealed state forever, some a limited time.  Generally, 4130 CondA parts are usually heat treated to cond N state before use.  You can torch anneal metal.  

To Normalize 4130 is to bring it to the Cond N state that has been determined to be the optimum hardness, strength, ductility for aircraft use.  This is a 95,000PSI tensile strength condition.  Yes, an airframe joint can be torch normalized.  It must be done carefully.  The metal should be brought to a dull red and let cool slowly in very still air that is not cold air.  Normalizing will not relieve stresses in the frame do to mis alignment, twist etc. because you don't heat the metal enough to bulge or neck down.  The idea of torch normalizing as it applies to our type structures is to try and remove hardness near the weld and improve ductility near the weld.  

All of these processes take some skill and care to do properly.  Done wrong, you can ruin the grain structure of the 4130 resulting an a weakened structure.  This is why most "experts" advise against these proceedures with respect to homebuilders.  Basically, you know what you have at the point of completing the weld.  If you heat the joint, you may or may not have damaged the material.  Bird in the hand!!!  This is kinda like the fabric covering manuals.  It is far better to tell beginners "Don't or Never" rather than say "you can here but not there" because someone will use the wrong tool in the wrong place and f --- up the job.  Same thing here, Finch says "don't" to try and keep a do-it-yourself-er from ruining his parts.

Now, one thing to keep in mind is that all these welding books and videos are basing their info on good welds.  Not crappy ones.  Welds MUST be smooth, neat and flow gently into the parent metal.  Globs, lumps, undercuts, and generally nasty looking welds are in no way as strong as the pretty, neat ones shown in the books and videos.  Making the weld bead bigger is not a savior for a nasty weld.  Weld engineering is a huge science.  Whether you use gas, tig or mig, doing it wrong will ruin the structure.  I have seen some TIG welds that are nastier looking than Beginner workshop Gas welds.  If it looks bad, chances are it is bad.  I have seen alot of welds that looked ok to the eye but were not stuck!  Some think more heat is better.  Wrong!  It can ruin the base metal.  Practice, practice, practice until your welds are good enough and look good enough to pass a weld certification test.  Then build.  After all, you can't just pull over to the side of the airway when your airplane breaks!  KKI


I have a question about the pictured weld bead: weldbead.jpg. Sometimes I get lines that look like stars on the "stack of dimes", and sometimes I don't. Do you know what causes the lines, and how I can avoid it? Is it something to worry about?   Thanks, Darin
Not to worry about the 'star look' in the welds.  It is a factor of temp.  You are only slightly hot.  If you are using the 80s-d2 rod, the weld will have the golden to copper color streaks in it.  A little too hot and you get the stars.  But you are not way over hot in what I see.  That is a difficult spot, thick to thin.  KK


I've been practicing my welding on fishmouth joints, in preparation of making my longerons. Like a lap joint, it seems that not much rod is needed and none at all if the outer tube is more than .035 wall.   On the bungs I got pre-welded from Kevin, it looks like no rod was used. The outer tube on them is .120" wall.   Question: Should I be using rod to add a more ductile alloy to the weld, or is it ok to just melt the 4130 together?   Thanks,  Darin
The parts you got from us DID have filler rod used.  We make an effort to bring the filler rod up to the outer surface of the outer tube.  In this case, 1.25"x.120 tube.  Why?  So the entire thickness of the outer tube is working.  The filler rod is softer than the base metal 4130.  Both the filler rod and the base metal are hardened by the welding process.  To seam the parts together is a no-no as the joint will be nearly 2 times as brittle as it started out.  Also, you will get some undercut in the base metal which is a bad thing too.  I can telll you that there is not a single 'seamed joint" in the entire set of model 12 kits we sell with one exception.  The end caps on the seat cross tubes and the front end of the Torque tube.  We use 3 sizes of filler rod.  0.045", 1/16", 3/32" all are ER80s-D2 3 ft cut copper coated.  On the bungs you got from us, we used 3/32! " filler.   We use about 4 or 5 sticks of .045 on a batch of 6 model 12s.  Not much.  You can most likely get by without it.  It is handy on some of the very tiny stuff. KK

10/18/00 WELDING ROD, ER80S-D2

Kevin,  I am ready to order some ER80S-D2 welding rod.  Could you give me an estimation of how much of what size I will need?  Thanks, Steve
You can do all the welding with 1/16" rod but some .045" is nice to have on the small stuff. A 10lb box of 1/16" is more than enough. A lb or 2 of .045" if you can get it. We use about 20lb of 1/16" and about 2lb of .045" in welding all the parts for 6 model 12s.   KK


I have just finished welding the basic fuselage truss on my Super Stinker and I am trying to figure out the best way to post heat the frame. What I would like to do is post heat the truss first, support the upper wing in position then build the cabane and weld it in place while the bushings are attached to the wing.  After the cabane is attached I will go back and post heat it.  Can anyone see any inherent flaws in my thinking?  Any advise will be appreciated.  Mike Groft
I suggest no post heat for the entire fuselage.  We only post heat a few spots on the Model 12 frames.  Like the lower wing attach fittings, engine mount bungs, cabane fittings.  If we were to torch all the joints in the frame, we would twist it up to the point it would not be acceptable.  To totally post heat the frame, you would have to have a class A fixture and am oven large enough for the entire frame and jig.  

I suggest you use the rosebud to warm the lower wing fittings, etc and that's all.  KK
Thanks for the reply Kevin, The reason that I was going to post heat everything is that I still do not have the current down perfectly during welding and my welds don't have that golden color you told me about before (at least not all of them). I know for a fact the penetration is good and the welds are sound (don't know how many I cut apart before I started) but I did use too much current and I want to make sure they aren't too brittle. Should I be concerned? I'm already set up to secure my fuselage and rig the wings. I'm using a very similar setup to what you suggested. Mike
Mike, With the effort you put forth in learning and testing your welds prior to starting, I'd bet all the welds are fine. Many things other than amperage can affect the color of the weld. Recall that the weld joints in Curtis Pitts designs are all expected to be 80% efficient. That is, 80% perfect. If you have that minimum, the joints will exceed the tube. We always try for 100% perfect welds to have the good feeling of the extra 20% safety factor. KK


Should I still do a 4 point tack at the longeron joints that will require bending, or just two tacks on the axis of the bend?   Thanks,  Darin
I use 2 tacks per tube end all over.  place them where you can get the bends done. KK


I am using a LA-9 torch which came with it and also am using a #6 cup on a gas lense. It seems like the pink cup IS what is keeping me from getting in there better. The gas lense cups all seem to be the same diameter with just the hole size different. It sounds like I need to switch back to a small collet setup. I didn't realize that the cups that go along with collets varied in diameter.  I'm going to check out what other torches are available too. I like your advice about driving the pedal, maybe I'll dust off the old twister game mat and take it out to the welding area.....Darin
What size pink cup are you using?  Are you using collet bodies or gas lenses(screen)?  We use a #6 cup on most everything.  But sometimes use a #5 on tight stuff with the tungsten out 1/2" or so and never really adjust the gas flow for that.  If you are using a gas lense, it is alot bigger than a collet body and the pink cup is much bigger too.  We don't use the gas lense as they are too large and on this type work, have minimal benefits over collet bodies.  Another question is what size torch do you have?  DO you have a thumb control or foot?  We have HW-20 torches.  The smallest water cooled one made.  Smaller is better.  If you a a HW-18 size torch, that could be too big.  I used a thumb control for the very first time(and hopefully last), this past week end while welding some stuff in WI.  That thing is a pain in the butt and makes the torch very hard to handle as well as having that darn box sticking out.  The foot pedal is the best way to go.  Learn to drive it with both feet, your knee, your thigh, your ribcage.  That way the torch is small and light.  KK


Don't need to remove the copper from the rod.  We don't cut the end off the rod when welding steel.  Found it makes no difference.  We do cut the end when welding aluminum only. 

We don't clean or sand the tubes with anything.  Heck the insides are still only from the nibble and cutting process.  All that cleaning makes about a 1.5% difference in the weld look and quality.  You will like the ER80SD2 better but it won't improve the look of the welds.  Technique and many hrs of practice to get it looking real good. 

Looked at your welds on your site.  Not bad.  Goal is to get the weld to be concave in the corner not convex or a simple wedge look.  Looking at your tungsten, I'd say you don't have a long enough point on it.  We make the taper 1/4" long on a 1/16 tungsten and have that entire tapered part beyond the end of the pink cup.  15 to 16 on the flow-rator too.  You want the beads to look like a stack of dimes that you tipped over.  Only about 1/16" from dime to dime.  On a 1" tube joint like to ones you show, about 1/8" of weld on each tube is good.  Keep sniffin' argon!!!  KK


When I first started welding tubes I had some problems right off the bat. No matter what I tried it seemed I had a contamination problem. It first showed up as foaming metal around the edges of the weld. Also the tungsten would turn blue well up into the cup.

After much head scratching, troubleshooting and some key help from some guys on a welding newsgroup, it turns out I had a bad bottle of argon! Who would have thought my first bottle would be bad. The guy at the welding supply said that sometimes when they fill the cylinder they don't pull enough vacuum before filling the cylinder.

I switched cylinders and no problems since. Also, I discovered I get similar symptoms when the bottle needs replacing too. I change out the big bottles of argon when they get down to 200 psi or so, thus avoiding problems. Darin


Kevin, what type of torch do you guys use, do you use one of those flexible head ones?
We use a HW-20 torch.  Not a flex head just the small 250amp watercoolered one.  You should ask Bud(howard) Clark in the group what tourch he has as he has the same welder as you and has built his fuse.

Are you using gas lenses or collet bodies?  The Pink thing on the outside is the ceramic cup and it fits both a gas lense and a collet body.  Gas lenses are better but bulky.  We use collet bodies.  As for the ceramic cup, I use a # 6 almost all the time with 16cfm of gas.  Be sure to flow gas before and after the arc starts/stops..  Using a #5 or 4 cup will speed up the gas too much and result in a a weld that is not as good as with a #6.  Use the small ones only in special tight places.  KK
My welder only came with a 1/2 cup on a 3/32 collet body. I just switched to a gas lense and will use the #6 cup. Are you guys using a 1/16 tungsten too or smaller one? I may also get some of the smaller collets to try them out too.
1/16" 2% thorated tungsten with 1/16" collet, collet body and #6 cup is what we use for 95% of our welding and I would say that 100% of a model 12 or skybolt frame could be welded with this setup.  I use 1/16" pure tungsten for alum welding.  KK


After awhile the machine (Lincoln Square Wave 175) wouldn't start an arc. I would push on the pedal and the machine would make the usual noises (HF)  but no arc. I would shut it off, play with the ground clamp and try again and it would usually work. Then after a few more days it wouldn't work at all. I thought maybe it was a grounding clamp problem but couldn't even start an arc on the clamp itself. I didn't think  to try a scratch start.  I took the machine to a warranty repair shop and  the machine checked out fine, they said it welded great. They guy at the shop told me that I might have a gas flow problem and I should try using a gas lense. He said that the arc would be difficult to start without a good gas shield.

I took the machine home and it has welded just fine for about 10 welds or so (I don't get a lot of time to practice right now) but last night it wouldn't start an arc again. I tried scratch starting an arc. Although I wasn't able to start an arc, I think it would have judging by how well the tungsten stuck to the plate! The machine was off for a few minutes while I reground my tungsten. After that it worked ok for the 3 other passes I made last night.  Thanks in advance, Darin
I have noticed on the Small TIG units that the High freq generators are not as powerful as big TIG units. Whenever you stop welding on DC there is a small cloud of  ionized metal particles around the tungsten. These tend to condense on the tungsten as it cools causing a very thin metal oxide layer to form. This layer is a very good insulator. The trick around this is to cold scratch the tungsten on the metal before applying any power. This physically breaks through the oxide layer so your arc can initiate.  Ernie Leimkuhler

05/04/00 WELDING ROD

The guys at Lincoln were recommending that I use ER70S-2, which is what I've been practicing with. They said it has more flexibilty in the finished weld than 4130 filler rod. Any thoughts?   Note:Lincoln has since changed its recommendation to ER80S-D2 also.
ER70s-2 is good for 4130 but you will find that ER80S-D2 is better giving you a nicer weld and allowing you to make multiple passes in those loose tube joints. KK