Need assistance in determining best welding option. What did most builders do?

[Airbourne111]

I have had to weld thin metals with mig. I can tell you that it makes one of the strongest and sweet joints. Takes practice, but once you get it right, you are good to go. Saves you lots of hours on the build gas/flux core.
when it comes to joints needing more penetration, adjust your wire feed and heat adequately.

Mind you I still own a Lincoln Electric Tig . And use it often

[spinningwrench]

I believe the Bearhawk factory will MIG tack a fuselage together and then re-melt the tacks with their OXY welding. This is a pretty handy approach as you can very quickly get a fuselage framed up. A MIG weld tends to not re-melt as easily as fresh welding rod so getting a re-melt can be tricky. I have watched and know the welders at American Champion where the bulk of the airframe is MIG welded. Those guys need to recertify every year as technique is very important for MIG welds which require a stitch welding approach. They actually use old school MIG welders which have been modified to give continuous gas flow between bursts. For the novice I would stick with TIG or OXY.

[unixxx]

If anyone is interested in comparing TIG and Gas welding for aircraft take a look at the book Performance Welding Handbook 2nd Ed by Finch. It has a chapter Comparing Welding Processes that mentions which welding processes were used in the manufacturer of various historical airplanes, including numerous examples of TIG and MIG. The author claims he was responsible for revising the welding section of AC 43.13-1A.

[fairchild1934]

I will chime in with my 2 Cents-----
either oxy or tig will be fine---- but for either one you will have to have a certain level of proficiency. Lots more grime and oxidation with oxy--- but it may be more forgiving as far as heat control on thin parts. Go and take a semester of training on either one and then you will know the basics.
That will give you real world practice and in person feedback from a teacher. That will give you help you wont get on your own. Ideally --- have both systems on hand. You can get a fairly inexpensive Tig setup used for 600-1000-$ (wont do aluminum) like a used miller maxstar. You wont need hardly any current capacity for tubing and sheet. The smallest maxstar or equivalent should work great. I think there are places for both types of welder when building a tubing fuselage.

[Redneckmech]

I will chime in with my 2 Cents-----
either oxy or tig will be fine---- but for either one you will have to have a certain level of proficiency. Lots more grime and oxidation with oxy--- but it may be more forgiving as far as heat control on thin parts. Go and take a semester of training on either one and then you will know the basics.
That will give you real world practice and in person feedback from a teacher. That will give you help you wont get on your own. Ideally --- have both systems on hand. You can get a fairly inexpensive Tig setup used for 600-1000-$ (wont do aluminum) like a used miller maxstar. You wont need hardly any current capacity for tubing and sheet. The smallest maxstar or equivalent should work great. I think there are places for both types of welder when building a tubing fuselage.

Good advice,
I did a one year community college program for my welding certificate long before I decided to build a Bearhawk. At the time, I think it was $600-800/semester and was money well spent. Several of the students there were retirees that wanted to learn welding for different reasons. Another consideration, is that many companies (Snap-On for instance) offer significant discounts on tools and equipment to students so you may be able to recoup the cost of tuition.

[fairchild1934]

i think my semester's tuition was like --- less than 200$. another bene of it -- was it gave me an idea of which brand and model of welder I wanted.
You kind of have to try them to tell i think. so it was a twofold gain. it was a trade school on the community college level.

[S Lathrop]

My 2 bits of advise. My background is 50 years in auto racing small bore formula racing cars. In that time I have help put 200 cars on the tracks for SCCA racing. About 100 of those cars had MIG welded frames and they were solid cars with very few frame cracking problems. Starting in the 1980's I switched to TIG welding. I spend many thousands of dollars trying to get MIG welding equipment that would give the the quality of TIG welded frames. No Luck.

My take away from all those years is that it takes very expensive MIG equipment and a very good welder to make good MIG welds in thin walled tubing. Also, I have never seen a successful repair of a stress crack in a frame with MIG equipment.

Bottom line, gas or TIG is the best option.

The Issue I see with a MIG weld is the shape of the weld bead. The center of the weld is quite thick and heavy. At the edges of the weld bead there is a very sudden change in the thickness of the weld. With gas and TIG you have a weld that has a very gentil transition from the edges of the weld bead to the base metal that is being welded.

[fairchild1934]

I think it just depends on which system you like better and feel like is more in your comfort zone----

[SpruceForest]

FWIW, the cost advantage of O/A is largely gone... inexpensive DC inverters machines and even some AC/DC TIG machines are under $600 with a 9 or 17 torch/hose, etc., which is less than what you'll pay for a new Smiths AW-1A O/A torch, regulators, a set of tips, safety valves, and light weight hose. Consumables are a wash, with the TIG system less on gases (acetylene and 02 not cheap), a little more for collets, cups, etc. for TIG, and RG-45/60 running about the same cost as ER80S-D2 and ER70 (for mild steel to 4130N). I have both O/A and TIG, and continue to get better by using both for anything I can (modified my TIG cart the day the Everlast 255XLT was delivered... using O/A... further mods with the Everest TIG).

[unixxx]

Do any of you proficient in both TIG and O/A have situations where you find the O/A gives better results?

Still learning TIG welding and having only tried O/A once, it seems O/A would give less control due to the force of the gas out of the nozzle.

Maybe there are cases where O/A's larger HAZ is helpful during the weld?

[Frank]

Budd Davisson always cheers me up. You probably saw his latest Shop Talk in Sport Aviation. I'll always remember him arguing tig vs. o/a at Oshkosh one year. And I never miss his webinar even though quite repetitive. This latest article offers tips on tube notching. Some relevant quotes:

"First a quick, and borderline controversial, discussion of TIG versus gas welding. Just let it be known that TIG is happiest with small gaps, super clean joints, and good equipment maintenance (tungsten care and all that). Basically, it’s more persnickety and less forgiving than gas, but much faster.

"Oxygen-acetylene is much less dependent on tight gaps, mostly because it’s easier to control the puddle and OA weld beads are always much wider. Better yet, once the bead is started, surface tension can keep the puddle intact over ridiculously wide gaps. We should try to keep gaps down, but occasional meanderings can be tolerated.

"The following comment is what’ll generate incoming emails: I personally think first-time builders will benefit from the more forgiving nature of OA. And it’s cheaper. However, that’s just me. And that’s a subject for a later Shop Talk. However, if you have TIG, by all means, use it."

[Frank]

My approach will be to start with o/a first, and attempt to fabricate steel parts for the wing. See how it goes. Then move on to tig if that looks like a good idea.

[unixxx]

Thanks Frank, that makes sense. During the TIG process, the puddle is small and the alignment and distance between the tungsten and work piece must be precise. I've heard other skilled welders also warn not to attempt to bridge gaps with TIG.

[Have-Purple]

I'm enrolled in the welding program at my local community College beginning in the new year. I figured I could knock it out while I wait for my companion QB kit.

One of the primary goals coming out of the class is to be able to construct a good fuel header tank out of aluminum for placement behind the baggage bulkhead to feed my proposed UL 520T motor.

The school is not even charging me tuition based on my Veteran status. If anyone has ever wanted to learn to weld, check out their local tech schools. The entire certificate program was less than $2k and they prep you for passing local employers weld tests. The school is fully stocked with new Miller equipment. It's a nice setup.

[unixxx]

That's awesome. I'm not aware of anything like that over here.

For those without the community college option, Lincoln Electric also offers classes in TIG, 4130, aluminum, etc:

https://classes.lincolnelectric.com/modules/

[Redneckmech]

This is an excellent approach, back when I was getting my weld certs there were several retirees that were in the class for assorted reasons. It is a very inexpensive way to get the needed knowledge and practice for a project such as this.

[rodsmith]

I believe it is best to learn O/A welding first before TIG. I also got training at a local community college, that was their preferred sequence, a semester of O/A before a semester of TIG. The courses were geared towards industrial welding, not aircraft. The instructor, same for both courses knew what my needs were and helped me develop skill in welding aircraft tubing and fittings.

[Redneckmech]

I agree wholeheartedly, oxyfuel welding teaches puddle control, teaches you to read the puddle, and directly translates to every other form of welding. Once you have the basics down with it, all other processes are just technique and practice.

[Redneckmech]

Do any of you proficient in both TIG and O/A have situations where you find the O/A gives better results?

Still learning TIG welding and having only tried O/A once, it seems O/A would give less control due to the force of the gas out of the nozzle.

Maybe there are cases where O/A's larger HAZ is helpful during the weld?

Frank summed it up pretty well above with Budd Davidson's quote but ultimately everything is a trade off.

Oxyfuel welding is better for bridging large gaps and is more tolerant of mill scale, rust, and other contaminants. Tig (If you want to use the current nomenclature GTAW) is much faster and as you mentioned has a smaller HAZ but with the thicknesses we are welding on a BH will not matter to a great extent provided best practices are followed. Tig can make a very small puddle/weld bead on thin material but that is NOT what we want to be doing, a very narrow tig weld will not have enough heat input which will in turn encourage martensite formation. I think this is one of the reasons Bob and others recommend oxyfuel welding over tig since there is enough heat input from oxyfuel that it eliminates that risk.

Ultimately it comes down to which process you are more comfortable and skilled with. My side job to support my aviation hobby (addiction?) is repairing aircraft fuselages for a local FBO where I typically use tig. Since you will be welding on clean new material and controlling your fit-up, either should provide great results as long you ensure that the weld joints are clean and have all mill scale removed. I am really looking forward to welding my fuselage since there are few things nicer than welding on new, clean, uncontaminated material!

A good weld starts with good preparation, cleanliness and fit-up are CRITICAL no matter which process you are using as they will dictate the final result.

With either process, ensure that the weld is not cooling quickly since this will encourage martensite formation and cause brittleness. This has been covered in great detail on this forum and elsewhere..

Here are a couple of obligatory pictures of a recent project I just finished up for the local FBO installing float fittings onto a Stinson 108-2. As part of it, we had to replace the last two feet of the lower longerons when I discovered internal corrosion (I have done the same thing on multiple other aircraft as well so it bears mentioning to make sure to drill witness holes between your fuselage members prior to welding and oil them internally when you are finished welding).

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[S Lathrop]

When I first was learning to weld, I was lucky enough to be close to several fabricators who gas welded aluminum as a regular business. Most of the work was done for race car body work where the welds would be hammered out and the part would be finished smooth. Because of the challenge, I learned to gas weld aluminum with O2 and acetylene gas. The preferred aluminum welding method was to use hydrogen gas and oxygen for aluminum but it can be done satisfactorily with acetylene. After that beginning, TIG was a snap to learn.

In my early years of race car construction we used aluminum tanks. Fuel cells were not required back them. The big advantage of gas welding aluminum is the back side or the weld is way better than TIG. The back side of the weld looks as good as the welded side with a smooth weld bead and a gradual taper to the welded material. A tig weld can come out this nice if you "back purge" the welded area with argon. But on flat sheets that is a hassle.

[rodsmith]

That is a skill I would like to learn. My attempts at oxy/acetylene aluminum welding ended in a melted mess. Great to have mentors.