Is it ok to tack weld with a stick then use oxy-acetyl to finish the job?

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trimtab

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Yes.

Although for the cost of O2 and acetylene gas on a project the size of a cub fuselage, you'll be halfway to paying for a reasonably nice TIG welder by the time you are done.

If you are even a marginally capable gas welder, TIG is a breeze.
 

wsimpso1

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I would not.

Let me give the technical explanation. Maybe we have someone with more background or detailed knowledge of AC43 that will chime in and destroy my whole commentary.

4130 is medium alloy, oil hardening steel. Anytime you take oil hardening steel from above 1330 F down to 500F or lower in less than 10 seconds (what an oil quench can achieve) you will form primary martensite, which is glass hard, under a lot of residual stress, and brittle. It must be tempered or welded through again and allowed to cool slowly to make a tough piece from it. Since most tack welds you will make with a stick welder will go from orange to dark in around a second, you can be assured that in 4130 they will contain martensite and are likely to have little cracks develop. Just to put a qualifier on all of this, it is standard aircraft welding practice to avoid drafts when welding to avoid brittle welds. If some moving air will produce substandard welds...

Some folks might say that they will later weld through the tack weld, re-melting that hard crack prone nugget and then get nominal cool down, so it is no big deal. If you can ALWAYS achieve that, terrific. But if you are human and do not re-melt all of tack welds when you go after the thing with an aircraft O-A torch and a rod, the ones that you do not melt through are likely to start cracks. Since we will have so many tack welds in an airplane, I am disinclined to do things that way. Some folks will also tell us that our welded joints are so overbuilt it won't matter. There is the story of a guy who stripped fabric from a Pitts for a recover, and discovered that he forgot to weld some of the parts - he had been doing acro for years on a tack welded airplane... Maybe a few teeny tiny cracks won't make a difference. All the same, I ascribe to the "let's just do it the right way" approach.

I gotta ask: If you have small gage plain carbon sticks and fine enough control to tack 0.035 tube with it, why not do the welds with that? Then you are almost assured of welding through the tacks, flux coating the welds to slow cooling, and using a machine you seem to be good with.

Billski
 

TFF

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Stick no. Kind of. Aeronca Champs were welded with stick, so you can’t blanket state it. The early ones had cracking welds so it took time to get the process right. When Champion took over they converted to MIG. Learned history repeated its self. Cracking welds until they got the process right. Some do it with MIG. The really good welders can tell when you get to the tack, when it’s electric. it is not as homogeneous melting. A stick on the thin tubing used in airplane, more than likely be a big hole. I have access to all types of welding machines. I usually pick the one I can get to work the easiest for the project. To me OA and TIG are the same. I’m a sucky enough welder that one is not better than the other. I pick TIG over OA usually for one reason, the flame. I helped in A&P school to get some of the students through welding that had never done it. I told one lady don’t point the torch at you. What did she do? Luckily it was just her sweatshirt. I put the shirt out and told her to turn it off. She never realizes she was on fire. Other than that I pick OA as it’s more versatile for one piece of equipment.
 

wsimpso1

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Yes.

Although for the cost of O2 and acetylene gas on a project the size of a cub fuselage, you'll be halfway to paying for a reasonably nice TIG welder by the time you are done.

If you are even a marginally capable gas welder, TIG is a breeze.
Let's start by saying this engineer disagrees.

I replied above on why I would not use stick equipment to tack a 4130 fuselage and follow with OA to do the welds.

A good used OA setup, regulators, torches, hoses, cart for safely moving it around, can be had in most markets for a couple hundred dollars. I have done it... Gas and rod for a competent OA welder to stay in practice and build a small airplane is about that much again. That is pretty modest dollars. You are going to spend a lot more money on decent a GTAW (TIG) just to get it in your shop, and it too uses money when you are welding with it - shielding gas and electricity require opening the wallet too.

Does TIG enable nice work? Yes, it does, but you also have to learn how to work it. There is a learning curve and requires some different technique. See the welding videos Little Scrapper has put up around here. Lots of good advice on training.

Given all the supposed advantages of TIG for production, you would think all factory welded kit parts would have to be TIG. Some are, some are not. The big handsome Pitts Model 12 fuselages, tails, and lots of internal hardware are made at their factory with OA. So are all of the Bearhawk fuselages and pieces you can get from the factory. It must have something besides romance to it that some commercial outfits use OA.

In the end, you get to open your wallet and choose. Both can make terrific little airplanes.

Billski
 

Pops

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Each type of welding is different and each one has its place. Experience with each will teach you which is best for you and your welding job. My least favorite is Mig. I have mig welded for years while working in steel fab shop, for my shop, I don't own one, but it has its place. I worked many years in building and maintenance in coal fired power planes in welding the boiler tubes with Tig and Stick and they are my favorite. I also enjoy OA welding but instead of welding with Mig, I'll use stick.
If I was building a steel tube fuselage on a low budget, I would buy and weld with OA . If I had a little extra money I would add the Tig.
I prefer tacking the tubing with Tig because its quicker and easy to make very small tacks for welding over latter when doing the compete welding.
 

Pale Bear

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Just curious, people, welding in any fashion, is trying not to cause any more harm to the joint, than one has to .. OA vs TIG, .. could it be said that TIG is a gentler process?
 

wsimpso1

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Gentle? you are talking about welding here. I once worked for an engineer very experienced in fabricated assemblies. "Welding f**** everything up."

TIG is not as hard on the steel, less total heat in the assembly, less distortion during and after the weld, less oxide scale, but it is welding - you have a puddle of steel at more than 2600F, and everything around it expands with the heat, and then has to contract afterwards.
 

Geraldc

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If you are welding with oa anyway what is the problem with tacking with it?You should have some form of jigging to hod the parts and that should be adequate to hold it enough for tacking.Another too I use for exhaust pipe work is aluminium tape. You wrap your joints and lift enough tape to get a tack on.
 

trimtab

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As a person that uses stick, gas, TIG, and MIG in my shop on a regular basis, and as someone who has had to have test joints sent out for eval on flight hardware with has and TIG, here is why I said it will be fine to tack with a stick and then use whatever method you find available to finish the joint.

Electric welding of any sort (GMAW, GTAW, or SMAW) has decades of heritage in aerospace flight hardware. Using a stick to tack has put tens of thousands of 4130 and mild steel truss fuselages in the air with AB and standard airworthiness certs. That's a difficult record to comport with a statement that approximates "it's a bad idea, and I'm an engineer".

Proper use of any process is essential. The Wag Aero fuselages were tacked via stick. How do I know? A gentleman from their factory at Oshkosh showed me when I was 14...tacked with a stick, finished with a stick (for the welded fuselage kits), and normalized with a torch. It was faster, stronger, and required more skill as I quickly found out from my gas welding background. The normalization is critical, and my own testing for coupon samples from certified aero welders has born that out...the stress relieving is important.

TIG is rarely viable from a production standpoint compared to MIG...and the various cub heritage models being fabbed all over bear this out today. Research the feed wire or filler wire as appropriate, don't use 4130 filler or wire, use a nice finish taper on MIG and TIG, and make nice thick fillets instead of anemic pretty ones. Normalize with a torch every few joints.

As far as strength goes, good welds from any of the processes yield similar results, as long as shield gas is adequate, taper is used to avoid pin holes for electric techniques, and as long as the flame is dead neutral for a torch...a carburizing flame is as poor a choice as an oxidizing flame.

As for costs, it costs me about $50 per hour of actual welding to torch weld on .082" steel. It's $140 per fill for both tanks. It's about $50 per hour of actual welding for the TIG argon or $65 for the argon/co2 for the MIG. At the end of each hour, I'll have 1x of weld from gas, 2x If weld from TIG, and easily 3x to 4x the length from MIG. You move fast with MIG.

Aluminum MIG is a lot faster than TIG...but almost requires a spooler. Nonetheless, the speed and cost savings leave large aluminum welding entirely to the MIG. With a TIG, the control you get allows welding soda cans together without difficulty. And I've never been successful with the gas welding systems for aluminum, although others have been.

Ultimately, following the guidelines for each process in steel will get you similar results for a coupon in an Instron tensile tester.

The OP has experience with gas. The transition to TIG is straightforward. The cost savings is real. A nice invertor multiprocess welder with TIG is around $800. Welding a fuselage with TIG will save a few hundred bucks or more in gas, and hours of time (argon, plus OA for normalizing).

Nonetheless, I still keep the gas gear around for cutting thick stock where the plasma cutter won't go, and normalizing, and brazing. It isn't costly to have around if you own the tanks.
 

Dana

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A stick on the thin tubing used in airplane, more than likely be a big hole.
Thatone
Doing the landing gear on my Starduster, I tacked it with gas ('cuz that's what I have) and my buddy finished it with TIG ('cuz that's what he has and likes).
 

wsimpso1

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There you have it. Tacks done on 4130 with a stick are OK. Doing the weld with any of the standards is OK. TIG will save a proficient welder some money on gas, but costs more up front. My concern about martensite in tack welds appears to not be an issue in 4130. Good to know.

I still gotta ask why the OP is tacking with stick but not planning to do the welds with stick? Seems like the natural progression to me, and the above experts say so too.

I have always found it interesting that we might weld with TIG, and justify it with higher production rates while welding and lower gas costs over OA. TIG has extra steps and materials - near perfect fitup, cleaning with abrasives and solvents of the metal and rods, normalizing the joints with a torch. Between the extra steps and materials, it seems to me we probably used up a lot of the savings. How does the total productivity and cost actually work out, including the prep and post weld work? Or is that what makes the commercial choice happen between the processes?

Billski
 

Pale Bear

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Gentle? you are talking about welding here. I once worked for an engineer very experienced in fabricated assemblies. "Welding f**** everything up."

TIG is not as hard on the steel, less total heat in the assembly, less distortion during and after the weld, less oxide scale, but it is welding - you have a puddle of steel at more than 2600F, and everything around it expands with the heat, and then has to contract afterwards.
Yes, .. that being my guess, as well. I've messed around with TIG, .. but, never with OA.
 

Ray Steele

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Recommend go to University library that has an engineering college. Find a book on aerospace by Brum. Then look up Society of Aerospace Engineers Welding Standard for 4130 and post weld heat treatment. There are several commercial heat treaters in the market place. Google for one's in your area. They have ovens and Good controls. They will want you to specify the heat treat recipie. Good luck. I've supervised welding & PWHT of 4130 for Ocean going ship parts, turrets, and superstructure.
 

fixnflyr

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Recommend go to University library that has an engineering college. Find a book on aerospace by Brum. Then look up Society of Aerospace Engineers Welding Standard for 4130 and post weld heat treatment. There are several commercial heat treaters in the market place. Google for one's in your area. They have ovens and Good controls. They will want you to specify the heat treat recipie. Good luck. I've supervised welding & PWHT of 4130 for Ocean going ship parts, turrets, and superstructure.
Most homebuilt and certified aircraft are designed and built without post heat treatment. It is not necessary to oven heat treat a fuselage after completing and is not cost effective. Also any oven heat treated parts will require another heat treatment cycle if repaired after entering into service. Most of the certified steel tube fuselages were never oven heat treated, although some of the landing gear parts on some light aircraft were (Luscombe).
This is not a jab at anyone but I would not mix welding standards. What is good for steel ship building is not the same or correct standard for aircraft construction.
 

TFF

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I know of a company that tried to heat treat a whole frame. It turned into a pretzel and some tubes collapsed, along with one of the jigs. One reason is the frame that big needs to be vented to breath. They were not going to do a recertification of the frame, so they dropped it.
 

Little Scrapper

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Threads like this easily get out of hand. We have a century of home building behind us and those men laid the foundation for all of us with great success. Your problem won’t be a bad weld. On the contrary, the data suggests you’re biggest issue will losing control while in flight, running out of gas or failure to preflight properly assuming you can finish the airplane.

Just do what we know works. Practice with some purpose and patience and weld it up using some supervision by someone who actually has done it. It would be wise to stick to O/A or TIG.
 
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Merlin

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I still gotta ask why the OP is tacking with stick but not planning to do the welds with stick? Seems like the natural progression to me, and the above experts say so too.
I'm not a welding expert by any standards, i read on various forum that using Oxy-Acetyl for fuslage was the only recomanded way to go as it has (supposedly) stronger welds and remove the need of any pre/post heat treatment to avoid cracks and tensions.
 

Merlin

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If you are welding with oa anyway what is the problem with tacking with it?You should have some form of jigging to hod the parts and that should be adequate to hold it enough for tacking.Another too I use for exhaust pipe work is aluminium tape. You wrap your joints and lift enough tape to get a tack on.
Tacking with a stick is faster, easyer, and more economical, also i wont have to heat the area i need to weld multiple times and possibly end up making it weak.
 
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