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02-11-2009, 09:22 PM #1
Oxy-acetylene welding aircraft frames....
Any experienced airframe welders here? I'm talking about the thin-wall 4130 type.
I'm interested in knowing what the "hot set-ups" are?
Best regulators, torches, filler wires (size and type), tips, gas pressures, etc.
I'm also interested in any tips, techniques, etc...
Any and all input appreciated. Thanks.
02-11-2009, 10:22 PM #2
GTAW on the 4130
02-11-2009, 10:29 PM #3
i dont think the gtaw is leagle on a/c. When i was in school in 91 we had to gas weld the old piper cubs. It might be now but gov regs are slow in the aircraft world
02-11-2009, 11:02 PM #4
My understanding is that oxy-acetylene is the preferred method.
I'd like to hear from those who are experienced in this, if there are any such people reading this.
02-11-2009, 11:23 PM #5
The guys at the rhinebeck aerodrome fabricated a replica spirit of st louis, using
I think 4130 and oxy/acet torch work. You might consider calling them up and
asking to speak to the welder who did the job.
02-12-2009, 12:34 AM #6
TIG is allowed, but you have to go back and normalize the structure at all the joints with an OA rosebud. If you have to break out the torch anyway, why not just weld it?
Any approved procedure can be used, if you know what that procedure is and have the paperwork to back it up. OA is the only certified field approved procedure for aircraft frame welding, as is. Actually, some Stinson frames were STICK welded! They had an approved procedure for that, though. Don't try this at home kids.
As for the torch, anything will work, but smaller is easier to handle, gets into tight places,and doesn't wear you out. A Purox 200 or similar will do anything you need. Ditto the guages. Victor, Smiths, Purox, Airco, any good name brand, so you can get parts. Pressure is a function of tip size, so look in the mfgrs book. My technique is to get a staright acetylene flame to stand just off the tip and back off a touch. Adjust oxy for neutral. Go just EVER so slightly to carburizing (I mean .01%, just a barely visible feather) to prevent oxidation due to regulator wander, and to cause the surface to melt slightly before the rest of the tube.
E70S filler rod, 1/16 diam, copper coated.
Main thing is to not overheat the tube or undercut.
I can explain this all day long, but it's like playing a piano. You have to practice to get good at it. You will not master it in a week, but it is a skill you can learn. For cheap practice, before burning up a bunch of 4130, play with EMT. Just wire brush off the galvanizing about 2" back and have at it. Thickness is similar and it's a little easier to heat without blowing through.
Start with simple Ts, then angles, then clusters, etc... Learn to fishmouth with a grinder, or my personal fave, a horizontal mill with an appropriate sized endmill and swivel vise. Once you can work with that stuff without it blowing holes, find some scrap airplane frame and cut it up... repeat. When you can make it look good, build an airplane.
I would suggest seeking out an EAA chapter near you (much as I despise the money grubbing establishment of EAA) and seeing if you can get with an experienced welder for some one on one. There are chapters al over that area, so just go seek out the local airport bums and ask.
I spent 15yrs at an aviation museum, starting in the restoration dept as a volunteer and working up to practically running the place. I learned from a 70yr old IA who could OA weld as well as anyone I have seen in my life. If you are good with a torch, you can weld using any method.
02-12-2009, 12:39 AM #7
GTAW (Tig) is by far the best, but even wire feed works. Method is not grounds for rejection, only quality.
You are likely already too old to pick up Gas welding in time to ever fly anything you build, I know I am. Your weld coupons need to pass! practice, practice build your own library of tips and filler.
I haven't turned my hand to it for over 25 years, so.... "what was I trying to remember? ;-)
Get a copy of "Performance Welding" Lots of good stuff, many Aviation examples. That reminds me, I need to get my copy back!
Mike said it SOO much better!
Last edited by CalG; 02-12-2009 at 12:42 AM. Reason: Praise
02-12-2009, 12:51 AM #8
Thanks, Cal. It's the FIRST thing I wanted to learn when I started at the museum. It's a very hard earned skill and one I am very thankful of being taught.
Method IS grounds for rejection, if proper procedure is not complied with. Been three years away now, but I think the last word is AC-4313, an FAA advisory circular booklet that lays down all the rules.
02-12-2009, 01:38 AM #9
Gas welding without "proper procedure" wouldn't make it past the AI either. I'm just saying, that done correctly, many methods or joining tubes could be and have been applied to aircraft construction. We are both saying the same thing. (practice, practice, keep your eye on the melt, Practice some more!) This is fun stuff!
My own experience is three years straight at the weld bench fabricating assemblies for commercial aircraft. Lots of TIG time. Then I moved on to program management. Hmmm Not sure if that was up or not ;-)
My copy of AC 4313 is boxed in the loft. "Acceptable methods of modification and repair for aircraft structures" the A&P go to book. Another one to dig out again.
Oh, and after working Aviation for 10 years, I started in Vacuum applications. Now the welds needed to be "perfect". "Please pass the TIG torch" Keep that tungsten Clean, NO dipping!
Last edited by CalG; 02-12-2009 at 01:43 AM. Reason: typo (one of them ;-) addendum
02-12-2009, 02:00 AM #10
Oh, given the choice, I'll certainly take the TIG myself, but I know the AI I learned from, who was also legal to sign off homebuilts, wouldn't sign off the motor mount on your new RV-10 if you had perfect TIG welds that had not been normalized.
As you know, you can do a perfect job of the task given you on the A&P test and fail it, if you do not break out the manual, look at the procedure, and follow it precisely. Same with the welding. That's what separates aircraft from other simpler repairs like motorcycles and cars. The job is no harder, but it has to be done by the book or it's your butt in a sling.
I really miss working on airplanes, but at the museum, I was not doing it truly full time, so it didn't count towards my A&P. With liability like it is today, I'm not sure I'd want to make a living working on planes anyway. Very few owners will spend money to keep them fixed up right, preferring to push the rules as far as possible to get out cheap. If one falls out of the sky and you name is on the books, better go ahead and call a lawyer, even if it wasn't your work. Not a lot of money in it, either.
One thing I found about TIG (same guy who taught me gas welding taught me TIG, I already knew stick from industrial construction), is how much better a OA welder it makes you. It just makes the puddle concept so clear. Conversely, I find OA helps you with TIG in learning heat control. Then you just have to get it straight... back out to cool it off, or back off on the pedal? lol. Find yourself spreading the puddle with TIG and stomping on the floor with the torch until you get the habits down.
02-12-2009, 08:09 AM #11
Ahhh...now we're talking. Thanks.
I'm a welding instructor/self-employed welder and I have a student that signed up for a night course to learn oxy-acetylene welding. He wants to build an airplane.
Thirty-plus years ago, I gas welded everything because that's the set-up I could afford, that's how I learned to weld. Still have my old Sears Craftsman kit that I bought new as a teen-ager. I believe it's made by Harris. I used to be pretty good with a gas torch. I did lots of stuff with oxy-acetylene that I'd never consider doing nowadays...I'd grab my TIG torch or MIG gun.
But, once I got ASME certified for pressure vessel TIG and MIG welding, I sort of abandoned my oxy-acetylene set-up except for brazing, cutting, and heating. Nowadays, my "bread and butter" is SMAW, GTAW, GMAW, and FCAW.
My interest here is mainly to help my student with any "tricks or tips" pertaining to OFW. I already own Performance Welding and a few other Richard Finch books.
Thanks for the help.
02-12-2009, 10:07 AM #12
is a good article.
is nearby your location (I think so,but, please update your location)
and was offering classes for gas welding airframes.
02-12-2009, 10:25 AM #13
OA welding 4130 aircraft frames
Great Topic to applies to more than just airplanes: I Hold an AP, like so many, and OA welding was taught inthe training back in 1970s. Was perhaps my strength area as I had study to be a welding engineer before starting the AP program. In my simple view practice first on good quality mild steel .030 -.040 sheet first. Good quality is material made in the USA that has the free sulfer controlled to a standard.
Start with, butt joints,then advance to tee joints ( fillet welds) lap weld and cornor welds. Must get this down to zero undercut, excellent heat control, bead width, penetration and apperance. Master thin section flat work first, as the tube weld is nothing more than all of these joints in one. . Oh yes, in all positions. Start sitting at a bench, and then move to sitting on the floor and welding under the bench.! Then move to tubing.
As for equipment, very important: Regulators must hold a percise flame as indicated. Very important. As for brands of torches, well that is also fun: I have a Victor Aircraft or J series torch. My friend has a Smiths Aircraft torch. There is not a week that passes the we do not tell each other to trade up and scrap each other's equipment! I learned on a Smith Torch and they are excellent. But I have Victor torch- and it is excellent. Nice to have a choice.
Most important point to consider and maintain is the condition of the torch. Valves must be tight thus maintaining the nutral flame or ever so slightly on the carbon side as clearly indicated. Never - never the other way to an oxygen rich flame. Tips are important: I keep a set of tips just for 4130 tubing work: Tips must be clean, and the flame cone must be maintained. In cluster joints the tips take a beating and must be keep super clean with each weld joint.
Years back sodium filled tips were on the market to help tip cooling, but I have not seen them for years.
Filler material, again must be keep clean, E70s of the highest quality wich is mild steel is what makes it all work. Do not use 4130 rod as that will produce a joint that must be heat treated or normalized and will crack. Big no go here.
Joint fit up: I would say an area that is as important as the weld it self. Joints have to fit, parts have to fit, not to tight thush placing pressure on tubing that will warp when welding heat is applied. Gaps must be avoided. Even fitting joints, pride on how the joints are cut, full strength and thickness must be maintained as the edges of the joint rotated 360 degree from a 100% fillet weld to what on the tips of the tube becomes almost a lap weld.
Joint fit up this is an art to master. Joints must be clean and free from any and all oil before welding. I do not like to grind a finish joint, grind or rough out Ok, but the finial fit is with a file, to prevent transfer of abrasive materials. On this same note, I suggest avoiding any type of blasting the joint before welding. Tubing is best welded clean and certainly free from anything like rust. If you use end mills or hole saws to cut joints avoid the use of sulfer cutting fludids, as they find their way back to the weld joint. Cutting joints with end mills is the best way, but does not always work and certainly hard for field work.
Blasting always gets material in the tubing and during the welding process finds it way to the weld joint. I know there is many great ideas here, and in industrial applications with the correct blast media weld joints can become super clean. But that is a complete new topic with many smart guys out there. Avoid any foreign material added to the weld joint is what I am trying to say.
Grinders, sanders, burrs, lock them up and toss out the keys. Wire brushes must be clean and stainless steel. Keep using fresh brushes, clean as you go on the joints, and just before welding brush and wash with a cleaner to remove oils and oxides, even oils from ones hands can be detected in inspection processes.
Plan your welding sequence to eliminate as many starts and stops as possible. Starts and stops must be mastered, again no undercut but no excesive build up either.
Once welded leave the joint alone: Do not go back and reweld, do not grind and sand to make the weld "look nice" that has to be accomplished as welded. Bad welds, take the entire thing out and start over. Excessive heat zones and reheating a joint must be avoided.
Tubing welding is fun and one can have a great deal of pride in the work. Take your time, plan your work and think about what the application of heat does to the airframe. Support joints, avoid welding on fire bricks or stone, as foreign material transfer to the joints.
TIG welding is another subject - but the same ideas apply. Torch welding is fun, slow but an art that can be mastered. My two cents on the topic. I would like to hear from others as there are many very smart guys out there who practice this each and every day.
02-12-2009, 12:07 PM #14
Did a lot of OA welding many years ago on ammonia tanks in the mid-west. You all are right about two things - practice makes perfect, & cleanliness.
02-12-2009, 12:26 PM #15
I don't consider myself an expert but there are some experts in the links below. I know that Air Tractor tigs everything. Only some of their highly stressed items get normalized.
All of the extra brackets and stuff on my Piper Cub project I tig welded.
Couple of pics:
02-12-2009, 01:00 PM #16
02-12-2009, 10:15 PM #17
"I know that Air Tractor tigs everything. Only some of their highly stressed items get normalized."
Just like the stick welded Stinson frames, that is part of their manufacturing procedure certification. Try stick welding a Stinson back together and getting it signed off.
BTW, NICE cluster weld there, sir!