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Creating a topic here to move the discussion out of a classified advertisement. Please feel free to continue the discussion here, civilly of course. 
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Christopher Owens
Bearhawk 4-Place Scratch Built, Plans 991
Bearhawk Patrol Scratch Built, Plans P313
Germantown, Wisconsin, USA -
Generally you don't mig 4130. TIG or oxy acetylene only. Mig needs to be pre heated, tig can use it to but puts a lot less heat into the material. Oxy is preferred.Originally posted by Stolguy
I probably would not consider a mig fuselage for anything but scrap. -
MIG is a perfectly acceptable method as long as it is done by a professional with experience...and by experience I'm not talking about making farm implements or repairing mufflers. American Champion and Maule MIG their fuselages, but it is done by skilled people trained in the process. Here's a thread that explains it a bit further, and of course always brings up discussion: http://eaaforums.org/showthread.php?...130-fuse/page2
As a general statement, I would say the majority of people on this forum do not have the welding skills to MIG an aircraft structure. On the other hand, saying that anything MIG welded should be regarded as scrap is a bit much.Last edited by alaskabearhawk; 05-13-2019, 02:57 PM.Comment
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As a retired welder (taught oxy/gas welding for several years in Part 147 A&P school and currently hold AWS TIG certifications for structural steel and aluminum) and A&P (40 years last June), I want to reinforce and support this comment. I do not have any idea who "Alaskabearhawk" is, but he seems to know what he is talking about.
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If all that was MIG welded was tabs and stringer standoffs I wouldn't have any concern at all. If landing gear and wing attach fittings etc were MIG welded I would want a qualified aircraft welding inspector take a look at them unless it was an aircraft welder that did the MIG work.Originally posted by alaskabearhawk View PostComment
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Ever time one of these post about welding gets posted, everyone throws in there two cents. We are not talking mig in general we are talking about the work done on this frame. This was just a farm blacksmith shop that mig welded the fittings . No post heat No preheat. . Not aircraft welder type people. I am sure the welds look nice but could be a problem, I even went as far as calling Randy Schitter at Rans aircraft in Hays Kansas . He told me they mig there frames . BUT they have the rite welder and Heat and wire OD for the job. No It is not just a mig weld job. He said aircraft tube is super thing way easyer to stress around the weld than something like a race car frame.Comment
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The reason I have that feeling is because the only way I'd get into a homebuilt with a MIG welded frame would be if the factory did it or I personally knew the welder and their ability. If I was a perspective buyer of a completed homebuilt and you told me/I saw the frame was MIG welded(and again that wasn't the factory), I wouldn't touch it with a 10ft pole for fear it'd kill me. No resale value at all.Originally posted by alaskabearhawk View Post
The fact that Mark has the fuselages O/A welded is a big selling point to me.Comment
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That is what Bob wanted. He prefers O/A welding of 4130 to other processes. MarkComment
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Could you heat treat all the welds with a tourch ?Comment
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Yes. To 1100F and "allowed to cool in still air". You could do it with MAP or propane even.Comment
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For anyone interested in the FAA's opinion, the Aircraft maintenance technician's handbook vol 1 chapter 5 is on welding. They go over recommendations for 4130 using O/A and TIG. Post heat treating is recommended even for TIG. Pre-heating to 3-400 over .120 as well. If you use 4130 filler, preheat everything. 1100-1200F for 45 minutes per inch of metal thickness. About 2.5 minutes on our tubing.
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In the MIG vs. TIG discussion, one detail that is critical to consider is the type of machines that are being used. Your Harbor Freight MIG machine and a top end Miller or Lincoln machine are as different as night and day in the welds they make. The aircraft manufacturers that are using MIG are using very high end equipment. The shield gas is also critical to the weld quality and the standard MIG gas is not optimal.
I have owned 3 different types of TIG machines over the decades and they all were different to weld with. My current machine is the only one I can weld .032 aluminum and .020 steel. I recently did some research on MIG machines to do some race car chassis where cost was going to be a big issue. The chassis would be largely mild steel, 18 gauge, and some 4130 in heavier wall thicknesses. That is when I got an education on the differences in the various MIG machines. In the 1970's I tried to use MIG on race car chassis and I did not have much success. While I had good equipment, I know know that it was not the right equipment.Comment
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If you take the TIG welding class from Mr. TIG (Wyatt Swain) at the EAA headquarters he will tell you that pre-heating or post heating welds less than .120" thick is not required. This is also the official line from Miller welding engineers when talking about 4130. TIG is generally the preferred process for race car frames. OXY welding puts a tremendous amount more heat into a weld than TIG with the subsequent distortion to deal with. OXY is a good process but pretty much abandoned from a modern welding perspective as TIG has pretty much eclipsed it. I am not saying OXY is wrong. I know the welders at American Champion. MIG is used for much of the airframe typically with an ER70S2 filler metal. MIG requires really good technique, generally doing a bit of a stitch weld. The most critical joints are TIG welded.Comment
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I have a big bowl of popcorn ready for this thread. Lurk and learn.Comment
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I know very little from personal experience as I do not weld. But my understanding is that TIG has replaced O/A welding for businesses because it can be done much faster than O/A welds. 100% true that O/A welding makes more distortion. But there are knowledgeable people, like Bob Barrows, who have really looked at it and prefer O/A welding for 4130 structures. Bob calls the shots at the kit factory. Both TIG & O/A welding are acceptable. MarkComment
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I know next-to-nothing about welding, save what I learned attending workshops at Oshkosh... What I can tell you is that I was doing sound (but really ugly) OA weld by the end of the welding workshop, as was my wife. We took it again the next day, and the instructor pronounced both of our results as "good enough to build a tube and fabric airframe." He knows more than I do, but let's just say that it was shortly after that that I plunked down the money with Mark G for a QB Patrol kit, in large measure because if I lived to be 100, my welds would NEVER look as good as the ones his factory guys produce... I'll weld stuff on my tractor, and I might even weld some angle iron together to build a swingset or something, but I'm not gonna trust my life to the quality of my OA welding skills!
As for TIG... We both took that workshop as well. I found it FAR more difficult, and in the somewhat overcrowded hand-on portion, never managed to get a single inch of weld that I felt was remotely acceptable. I did, however, manage to get one heck of a sunburn on a 1/4" wide strip of skin that was accidently left exposed to the UV light produced by the welding process! To me, TIG just was not fun, and my wife didn't even want to try the hands-on portion of the workshop.
It's been two years, and she's still bugging me to buy some OA welding equipment and some scrap metal she can play with... It's on the list...Jim Parker
Farmersville, TX (NE of Dallas)
RANS S-6ES (E-LSA) with Rotax 912ULS (100 HP)Comment
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