Selecting a Welder....

[DanH]

Originally Posted by akschu

Your argument that tig is stronger isn't in question, and I agree with everything you say in your thought experiment, however I don't think you really addressed the real issue which is different levels of hardness in adjacent structures which are subject to flexing and vibration. Ductile on an airplane can be a good thing as it tends to survive flexing and vibration without cracking better than something that is brittle, but especially better than something that has ductile right next to brittle.

I don't argue TIG is stronger. I argue strength is dependent on quench rate, regardless of welding method. And it's a change in the base material, not the weld; the recommended 70S-2 weld bead isn't hardenable.

Poor conclusions aside, the "break the tee" cantilever beam demonstration isn't applicable to tube fuselage structure.

As for fatigue resistance vs hardness....

[Ab&DaniRV-3]

Hello All,
As you probably know I am scratch building a -3. The early cowl that I have is longer than the cowls used today by about a inch and 1/2. The fact that I am using a C/S Hartzell, not the F/P with a 4 in. ext. I Decided to weld up a new Mount. Using the same material that I made the mount from, I made several Joints ..different angles and welded them together. Let them cool to room temp.(Like 90 in the shop). Then beat them brutally with a hammer. All of them broke next to the weld and through the weld. They took a lot to break, but should not have broke where they did. On many, tubing was bending before they broke. One broke before any noticeable bend of the tube. Next I welded some more up just like the first batch, using a no.2 tip, neutral flame 3/32 R-60 filller rod. This time the only thing I did different was left my flame on the weld after welding and brought the temp of the material down to a deep dark red over about a 1.5 min.span before taking the flame away. To my delight.. none of these welds broke. Tubing welded at a 45 deg. angle were pounded near parrallel. welds held up awesome but the tubing?... well scap price isn't high enough to recover any cost. I went this way of welding because of the cost and I have the set-up already. The new Mount looks AWESOME and now I can finally hang that engine and prop.

[robjohnson]

I have a small little inverter TIG from HTP, and I absolutely love it. I am scratch building a clipped-wing cub, and it has been fun learning to use, as well as actually fabricating with. Agree with DanH that there is a lot of hype on the web about post-weld normalization that is applicable in some smaller situations. But for welding an experimental aircraft made of thin walled 4130, the only drawback I see with TIG is the initial cost outlay.

Build progress can be seen at http://www.rv-builder.com

[rv7charlie]

Not sure if this as any use, other than as an analogy, but consider: anodizing cuts the fatigue life of aluminum by something like 50%. (All Van's wing spars for at least the last couple of decades have been anodized.)

What's most important, and what's good enough?

Charlie
(Miller Dynasty 200 that can weld a lot better than me, and a gas setup that can also weld a lot better than me)

[g zero]

I have and use on a regular basis a Miiler 165 Diversion , Tig is realy very economical as far as consumables go , and no flying sparks . You can go from alum. to steel with a flip of a switch .Also you can use the Argon to purge stainless tube with a inline Tee.
The Miller small inverter tigs come with a finger "throttle " and a foot pedal , when you plug the pedal in the finger throttle is disabled .
I picked my 165 up used , if I was purchasing new I would go with the 180 , not for more amps but can use 110 or 220 .As far as air vs water cooled the amount of actual welding time I do the air cooled has been fine .

I haven't touched my gas torch since I got the tig .

[jrs14855]

Pitts, Eagle and Husky Aircraft are TIG welded, NO repeat NO post weld treatment. That's all I need to know. Critics of TIG are dealing in theory not reality.
Ron Alexander wrote an excellent article in Sport Aviation about TIG welding, there was also an article on Aerotek with a lot of discussion on their welding techniques.
Those looking for a deal on TIG equipment consider the older Millers such as the Dialarc 250. Craigslist seems to be the best place to find used tools and equipment.

[rbibb]

My conclusion on all this is: There is a lot of science in welding (just check the technical journals). Tig is great, Oxy/Ace is great - if you know what you are doing. If you don't you can end up with a mess.

If I was just starting out in welding I'd get a good gas welding setup and learn that first. Why - because its cheaper and all the skills you learn will make you a better TIG welder. Now doing this in a garage or house calls for diligent attention to safety concerns lest one burn the house down as they say.

Then if you get good at it you might want to spring for a TIG welder cause its better at some things, probably faster, looks cooler, etc.

Sorta like if I was advising someone on learning to fly I'd suggest they master a J3 Cub if available for the invaluable lessons to be gained that is in it. Then they might want to upgrade their ride to something with a bit more juice....

YMMV.

I've got a Gas setup in the garage just begging me to get off my butt and put some of the lessons I got from a class taken years ago to use practicing so someday I might actually make something other than scrap. Only a few hundred tied up in the thing so I'm not too worried about it.

[rbibb]

Of course another way to look answer the question is this:

How to select a welder? Make sure they are certified in the process and materials you need welded. If she is good looking and can cook hire her.

[Ab&DaniRV-3]

Originally Posted by rbibb

Of course another way to look answer the question is this:

How to select a welder? Make sure they are certified in the process and materials you need welded. If she is good looking and can cook hire her.

Laughing my A** off!!!!!!!

[jrs14855]

Where the TIG is at its best is welding heavy parts to lighter structure. As for welding a typical steel tube fuselage I can do the job much faster with Oxy/Acy except for the real heavy stuff.
An example of where the TIG would work best on many RV's is the engine/landing gear mount on the taildraggers with round gear. This would probably take twice as long with Oxy/Acy not to mention the much worse distortion you would get with OA.