Selecting a Welder....

Yeah a thread about a welder on an RV message board... Really.

Actually while I was at OSH, I took a crash course on TIG welding with the Lincoln Electric folks. It was time well spent. I also took a class on gas welding, but it seemed a little primitive for some of the applications I could see myself using.

Thanks to a pair of misplaced #30 holes, I now have an opportunity to close them up with a weld and reposition them to the correct spot. I just got off the phone with ken@vans and he said the heat is no big deal on this specific part.

So I think I might be in the market for adding a TIG welder to the arsenal. I've got a ton of uses for it beyond airplane specific things.

So the question is which one do I want to buy? I'd like the opportunity to build a tube and fabric airplane at some point in the future (if it presents itself). How large of a welder would I need to get full penetration of a tube airframe?

Also, if anyone has any suggestions/experience on a specific model, please let me know.

Thanks,
Phil

Phil,
If you don't get good answers here, you might want to ask these same questions over on OSH365, if you haven't already. I know there have been some welding 101 type threads that might already cover the answers to your questions.

I've been having great fun with a Miller Dynasty 200 with a water cooled torch (http://www.millerwelds.com/products/tig/dynasty_200_series/) for the past year. It does just about everything I could imagine wanting to do right now.

The EAA did a webinar on welding with a guy from Lincoln. Of course he recommended one of their units. The cost of entry was in the $1500 range. It would do AC and DC with infinitely variable duty cycle. I don't remember the model, but I think you can view a recorded version of the webinar on the EAA web site. Anyway, there's no way I can justify that expense.

Let us know what you decide.

Clear skies,

Personally I don't care for the little TIG boxes because they don't have the duty cycle and amperage to do serious work, and they don't have the plumbing for water-cooled torches. I picked up a Syncrowave 350 on eBay for $750 with the chiller and everything, so if you are patient about looking there are bargains to be had.

Dynasty 200

I second the suggestion for the Miller Dynasty. I have a Miller Syncrowave 250 and it's a great welder but probably weighs 500 lbs or at least feels like it does. The Dynasty will do everything and more the Syncrowave will do and only weighs 45 lbs. Another advantage of the Dynasty is that you can plug it into anything from 115 single phase - 460 three phase.

Lincoln Electric Square Wave TIG 175

I bought the above unit several years ago and it provides everything I need. Most likely for what you will use it for that is plenty adequate. They discontinued it several years ago but brought it back because it seemed to be pretty popular. I believe the info packet you got at the seminar from Lincoln Electric has a rebate on that unit or others, also. Now that I have finished my RV-7A, I am learning to weld to work on the steel tube fuselage.

If I could give one word of unsolicited advice, practice for many hours prior to taking on your project. What you do in the controlled environment at the Lincoln Electric booth is far different than what happens in your home environment. The worst thing to do is to make a big hole out of a little one. I have ordered several boxes of scrap tubing from Aircraft Spruce and my welds while not looking good are at least less awful. That being said, welding is a blast!!!!

I also bought the commemerative(sp) EAA helmet and I love it.

Bill Near

Phil said:

So the question is which one do I want to buy? I'd like the opportunity to build a tube and fabric airplane at some point in the future (if it presents itself). How large of a welder would I need to get full penetration of a tube airframe?

Click to expand...

Just recently finished welding my first tube fuselage. Gas welding is still a preferred welding method for thin wall 4130 as is used in our airframes. It seems most fuses are made of 0.035" wall tubing which is pretty thin. The oxy-acet torch is a versatile device which can be used for welding a wide range of tubing thicknesses and has the built-in capacity of normalizing the carbon steel for max strength.

There is, however, much more art involved in making pretty welds than I have currently attained......... ......... but welding the fuse was an enjoyable project.

A few quick comments:

1. I prefer the Lincoln and have a Precision TIG 225. It's as big as you can go and get a air cooled torch.

2. You can get a big transformer based tig or a small compact inverter based tig. The difference is almost double the cost, but the inverter only weighs 40lbs and can weld on 115 or 230v without conversion.

3. Liquid cooled allows you to run a smaller torch and/or more amps which is nice.

4. You cannot weld 2024, so forget about filling holes in most aircraft sheet metal.

5. For building a fuse, I think gas welding is better. Tig looks nice, but requires much tighter gaps, doesn't fully heat a cluster, and can make the area around a joint brittle. So even if you tig, you should use a torch to normalize the metal after the weld.

6. You can gas well aluminum, and in many ways it's nicer than tig because you don't have to weld the backside. If you butt weld 5052 with a torch and flux, you can immediately take it over to the air hammer or wheel and roll the weld flat which allows you to polish the part.

I have a stick, tig, mig, and gas setup, and I find myself doing more and more gas welding when it comes to airplane stuff. If I weld on a tab or need something really small and precision, then I'll tig, but for everything else I'm moving over to gas.

If you want a great little gas rig, or just want more info, look no further than Tinman Technologies:

http://tinmantech.com/

Here is the meco torch I use:
http://tinmantech.com/html/meco_midget_torch.php

schu

Tube fuselage

What are you building Sam? I'm building a Marquart Charger.

Oxyacetylene welding is traditionally preferred for steel tube fuselage but TIG is rapidly taking over. I've done both and I prefer TIG

Bill Near

akschu said:

5. For building a fuse, I think gas welding is better. Tig looks nice, but requires much tighter gaps, doesn't fully heat a cluster, and can make the area around a joint brittle. So even if you tig, you should use a torch to normalize the metal after the weld.

If you want a great little gas rig, or just want more info, look no further than Tinman Technologies:

http://tinmantech.com/

Here is the meco torch I use:
http://tinmantech.com/html/meco_midget_torch.php

schu

Click to expand...

Yep, the Mecco Midget is what I use.

wjnmd said:

What are you building Sam? I'm building a Marquart Charger.

Oxyacetylene welding is traditionally preferred for steel tube fuselage but TIG is rapidly taking over. I've done both and I prefer TIG

Bill Near

Click to expand...

Just a little plunker for low-n-slow fun flying:

http://home.hiwaay.net/~sbuc/legaleagleXL/

I have to side with Sam here. While it takes some time to master, and it is often slower, the old-school stuff really shines when top-quality is considered. TIG can be brittle if not properly heat-treated. 75 year old oxy welds are as good today as when they were done. And while TIG and MIG have many uses, I use oxy for everything from jewelry work to cutting up I-beams. Everything has its place; pick what you feel comfortable with and learn to use it well. No one system will do it all.

My father was an aircraft welder for about 50 years. I wish I were that good...

Bob Kelly

Phil said:

So the question is which one do I want to buy? I'd like the opportunity to build a tube and fabric airplane at some point in the future (if it presents itself). How large of a welder would I need to get full penetration of a tube airframe?

Click to expand...

Specific to your question, size (or more precisely, amperage) will not be an issue in welding a tube airframe. Even the smallest units will do fine with thinwall steel. Power can quickly become an issue with thickwall (more than 0.125") aluminum.

The Lincoln 175 mentioned by Bill has been very popular with the biplane clan. I bought a Miller Econotig circa 1995, back when it was the first "home hobby use" unit in the marketplace. Today most would consider it a cripple, but I still get a huge amount of work out of it. At the other end of the scale
you can get as fancy as your wallet will allow. Regardless of your choice, you won't regret adding welding to your shop skills.

Gas vs TIG; learn both. Each will do welds the other won't. I usually suggest learning gas first and TIG later It's not critical, but a guy who has learned gas can pick up a TIG and weld well in minutes.

TIG is far safer for use in the typical attached garage home shop....no sparks.

Ignore 90% of what you hear about normalizing, crystalized metal, brittle welds, etc.

Postscript:
Had a dim memory of specs for the Lincoln 175 so I looked it up. Were I to buy a new Lincoln I'd want the Precision TIG 275 to get the tiny 2 amp arc. Yes, although more power is nice I've often wished for less. Both the Lincoln 175 and my old Miller only go down to 10 amps, a bit too much for some fine detail work with thin steel. Same is true for Miller....need to move up to a Dynasty unit to get amperage as low as 1 amp.

I'm with Sam on gas welding airplanes. I have both TIG and gas and use gas on almost all aircraft tube welds. If you use TIG you need a helmit (auto-dark is best) . Try welding in an awarkard position with the helmit banging around on the tubes and reaching for the pedal while working the torch and rod all at the same time, that is when you really like gas! TIG will make good welds, but I don't find it to be fun.

Not picking sides

I have both TIG and gas welders. After reading the discussions posted here, I went out to my hangar and played with both. I can see that both are worthwhile and require skill. While I don't profess to be a welding expert by any stretch of the imagination, what I have read and heard in welding seminars is that both are equally applicable in welding aircraft steel tube fuselages. However, based on this thread,and since I have access to both I plan on practicing both to hone my skills since I see that both require a similar set of skills.

Once again, whatever method you pick, welding is still a gas, so to speak.

Bill Near

For welding at higher power - like about 30 amps or more - I'd really recommend a water cooled torch.

Messing around with TIG is really fun, and you can do some really amazing things with the technology available today. Get someone who really knows how to weld to show you the ropes. I've thoroughly enjoyed my Syncrowave 250.

In the bearhawk manual there is a picture of two identical T shaped joints where the leg of the T was welded to the top. One was welded with gas and the other with tig. To test the joints, the leg of the T was bent back and forth until the tubing failed. The tig sample broke right at the joint after 2 bends back and forth, and the gas sample was very distorted but in tact after 6 bends.

The truth of the matter is that gas is the stronger weld in aircraft construction, however tig is without a doubt plenty strong enough.

schu

akschu said:

In the bearhawk manual there is a picture of two identical T shaped joints where the leg of the T was welded to the top. One was welded with gas and the other with tig. To test the joints, the leg of the T was bent back and forth until the tubing failed. The tig sample broke right at the joint after 2 bends back and forth, and the gas sample was very distorted but in tact after 6 bends. The truth of the matter is that gas is the stronger weld in aircraft construction, however tig is without a doubt plenty strong enough. schu

Click to expand...

An incomplete picture leading to an improper conclusion.

The welding process itself has little effect on strength. Given identical joints in 4130 but different weld processes, strength is mostly a function of postweld cooling rate. 4130 is an air-hardening steel; it becomes both harder and stronger when cooled more quickly.

Welding with gas tends to warm the tube mass for a considerable distance from the weld zone. In the case of that demonstration tee, all the tubing would quite hot, if not glowing. Postweld cooling is slow and even. The result is a more ductile assembly....but not greater strength. In truth it will reach its plastic region at a low stress level.

TIG tends to quickly raise temperature in the immediate weld zone without raising it a lot in the adjacent steel. Much of the tubing mass would remain cool (or not very warm), in particular if the operator was quick. When the weld is ended and the arc stopped, the adjacent cool sections serve to quench (rapidly cool) the weld area. The weld area becomes harder, less ductile, and stronger; it will withstand higher stress before reaching the plastic region, but the plastic region will be more narrow.

So, back to the picture. Have you ever actually done this demonstration for yourself? You should, but let's do it in the mind's eye right now.

First clamp the top of the gas welded tee in a vice, stem up. Attach a pound scale to the end of the stem and pull, recording how much force it takes to put a moderate permanent bend in the tube. Now repeat the same test using the TIG welded tee. You'll likely find the TIG sample takes more force to install the same permanent bend.....as much as double the force, depending on quench rate. The TIG sample is stronger.

Now lets pull the stem of the both tees back the other way so as to form similar permanent bends in the opposite direction. Then reverse again, and again if necessary. The gas-welded sample will indeed withstand multiple excursions into the plastic region of its stress vs elongation plot, but not the harder, stronger quenched TIG sample. It may only last for a few reversals before cracking. The TIG sample is less ductile.

You can make the demonstration more extreme.....just use a 4130 filler rod instead of something with lower hardenability like ER70S-2. It will sure enough pop right by the weld bead.

Now just for fun gas weld another tee. Even do your best postweld "stress relief".....but then toss it into a bucket of water while still very hot. Fish it out and do the bend test. Despite the weld process, you'll find it to be very strong but brittle. It may never take a permanent bend, instead just flexing like a spring.....and breaking with a snap when you force it too far.

It's all about temperatures and rate of change, not flame vs electric arc.

Yes, I've simplified a lot. So shoot me

DanH said:

An incomplete picture leading to an improper conclusion.

Click to expand...

DanH said:

The welding process itself has little effect on strength. Given identical joints in 4130 but different weld processes, strength is mostly a function of postweld cooling rate. 4130 is an air-hardening steel; it becomes both harder and stronger when cooled more quickly.

Click to expand...

Sure, however each welding process does produce a different postweld cooling rate and the concentration of heat is in different areas. This certainly can cause the finished product to have different modes of failure as illustrated by the test I mentioned.

DanH said:

Welding with gas tends to warm the tube mass for a considerable distance from the weld zone. In the case of that demonstration tee, all the tubing would quite hot, if not glowing. Postweld cooling is slow and even. The result is a more ductile assembly....but not greater strength. In truth it will reach its plastic region at a low stress level.

Click to expand...

Correct, but even more important is that the tensile strength is more uniform throughout the cluster. The problem isn't how ductile or brittle the metal is per se, but rather a ductile region next to a brittle region.

DanH said:

TIG tends to quickly raise temperature in the immediate weld zone without raising it a lot in the adjacent steel. Much of the tubing mass would remain cool (or not very warm), in particular if the operator was quick. When the weld is ended and the arc stopped, the adjacent cool sections serve to quench (rapidly cool) the weld area. The weld area becomes harder, less ductile, and stronger; it will withstand higher stress before reaching the plastic region, but the plastic region will be more narrow.

Click to expand...

Not only will the adjacent tubing cool the weld, but an air cooled tig torch is also cooled by the insulation gas which can cause the weld to quench faster than a normal in air quench, especially if the torch is left over the weld for any period of time which is taught to most tig operators as a way of keeping the weld clean.

DanH said:

So, back to the picture. Have you ever actually done this demonstration for yourself? You should, but let's do it in the mind's eye right now.

Click to expand...

No, I didn't see the need since it was done by people I trust, and it makes perfect sense. Anyway, I'm always game for a thought experiment.

DanH said:

First clamp the top of the gas welded tee in a vice, stem up. Attach a pound scale to the end of the stem and pull, recording how much force it takes to put a moderate permanent bend in the tube. Now repeat the same test using the TIG welded tee. You'll likely find the TIG sample takes more force to install the same permanent bend.....as much as double the force, depending on quench rate. The TIG sample is stronger.

Now lets pull the stem of the both tees back the other way so as to form similar permanent bends in the opposite direction. Then reverse again, and again if necessary. The gas-welded sample will indeed withstand multiple excursions into the plastic region of its stress vs elongation plot, but not the harder, stronger quenched TIG sample. It may only last for a few reversals before cracking. The TIG sample is less ductile.

You can make the demonstration more extreme.....just use a 4130 filler rod instead of something with lower hardenability like ER70S-2. It will sure enough pop right by the weld bead.

Now just for fun gas weld another tee. Even do your best postweld "stress relief".....but then toss it into a bucket of water while still very hot. Fish it out and do the bend test. Despite the weld process, you'll find it to be very strong but brittle. It may never take a permanent bend, instead just flexing like a spring.....and breaking with a snap when you force it too far.

It's all about temperatures and rate of change, not flame vs electric arc.

Yes, I've simplified a lot. So shoot me

Click to expand...

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.

The key to any metal work is to get the right material (including hardness) assembled in such a way where the forces placed on that metal do not exceed its yield strength. (Yes, I'm simplifying it a lot.)

In my opinion, (and in the opinion of a lot of other aircraft welders), tig welding causes an inconsistency in the hardness of the metal around the joint which probably won't ever cause anyone a problem, but why do it that way when the torch head is so much smaller, the head gear is so much smaller, and the cost of the equipment is so much less?

All of these things said, I wouldn't hesitate to fly in a tig welded airplane as long as I knew that the welder knew what he was doing.

schu

A tour of the Air Tractor factory was a great demonstration of welding process for me. A whole lot of TIG tubing in process there.

akschu said:

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.

Click to expand...

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....

OXY-acetylene welding

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.

Another vote for TIG

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

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)

Tig

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 .

TIG

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.

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.

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.

rbibb said:

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.

Click to expand...

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

TIG

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.

Jokes

The other variation is: Wanted: single woman with airplane and hangar, must be a good cook. Send pictures of airplane and hangar.

Be careful what you ask for here

Phil said:

Also, if anyone has any suggestions/experience on a specific model, please let me know.

Thanks,
Phil

Click to expand...

Hey Phil, Confused yet?

One other thing to think about in selecting a welder is to take the courses offered at the local community college. Most CCs have welding courses in gas tig stick mig. They also usually have multiple machines to try and instructors who are in the industry and are (hopefully) knowledgeable. After several semesters I was confident enough in my welds to fly behind them not to mention getting certified. Did I mention it was also fun!