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Playing With an Ancient Miller Piggyback High Frequency Start TIG Unit

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Robert LaLonde

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#1
I'm going to setup and test an ancient Miller piggy back high frequency TIG today. Of course in my early research everybody practically screamed that I have to use a DC CC power supply for it. Now that I understand the principles of where you use CC and where you use CV I get why it needs to be CC. HOWEVER, once I stated that I wanted to weld thin gage aluminum with it, that I can already easily weld (relatively) with my DC MIG from .080 to .25 and can do .375 if I preheat a few people grudgingly admitted that it might be possible (and maybe even better) to do thin gage aluminum with an AC CC power source. Add on that the piggyback machine itself is selectable for AC or DC and one or two more grudgingly said it might work.

Today I am going to test it out on some .0625 5052 sheet pieces I have laying around left over from various projects. I would have done it sooner, but I won't run one of my welders when any of the CNC machines are running. They run every day during the week. I've forgotten or lost focus once or twice and done it. I never had an issue, but I prefer to play it safe. Nothing like being 8hrs into a 9hr job and having your mill go haywire.

I picked up some 4043 TIG wire for 6061 and some 5356 TIG wire for 5052. I went through my drawer full of old gages and regulators and found a spare flow regulator so I don't have to yank one off my Miller 212. For now I will have to borrow the argon bottle off of it. I don't have any stainless bar stock for backing butt welds, but for just setting a little steel contamination won't matter. I'm just going to be working with scraps and making test welds if it works today.
 

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f350ca

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#3
I learned TIG on the exact same unit Bob. Well learned might be a stretch. Only used it on 1/8th to 1/4 aluminum, it worked beter than I could expect from what I knew. Thought it was AC input it wanted.

Greg
 
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Buffalo20

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#4
for years, NASA, did all of their critical aluminum welds, using DC.
 

Robert LaLonde

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I'd ask my grampa Robert La Londe Sr since he was a research mechanic for NASA (Lewis Research Center) until he retired back around 1980/81, but he has passed on.

From what I understand the advantage to AC welding aluminum is a reduced need to completely clean the material and remove the oxidation layer before welding because when it switches it electrode negative it has some cleaning affect, and when it switches back to electrode positive it welds better. I still intended to clean and brush, but I'll do some experiments with just cleaning without brushing too. I DC weld aluminum all the time with my MIG welder. It absolutely has to be cleaned and brushed and rebrushed if you walk away for a for more than an hour in order to get the best results. I'd really like a pulse MIG but the price tag is a little more than I can justify.

So here is the power source I'll be using to start with. I have not used this old AC cracker box in years. Right now the layer of crud is soaking in 409. There was just barely enough room to lift it out from behind my bolted down air compressor and between it and the air dryer. If this works I'll need to think of something else to store behind the air compressor. LOL.
 

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Robert LaLonde

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#6
Greg, Nope. As you can see its selectable source. I'd use a DC source if I was going to weld steel with it. In AC mode its HF continuous. In DC mode its HF start only.
 

Robert LaLonde

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#7
Wel, I took the cracker box apart to see if there was a nicer way to attach cables. Well, and to see if it had a copper or aluminum transformer since its at that age it could have gone either way. Sadly its an aluminum transformer. Anyway, I don't really like any of the options so I'm just going to cut the cables and put lugs on them. I'd hate shortening the cables like that if I ever used this welder anymore, but since I don't and this may give it new life I only dislike that solution.
 

Robert LaLonde

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#8
P.S. I've had the cracker box for over 20 years, and I finally took the boards off the bottom today.
 

f350ca

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Greg, Nope. As you can see its selectable source. I'd use a DC source if I was going to weld steel with it. In AC mode its HF continuous. In DC mode its HF start only.
Its probably 25 years since I used it Bob. Didn't remember it having the option. Was going to ask but you answered, thats pretty slick that it had the HF start for DC. Only ever welded aluminum with it. Having to turn the gas on with the knob was a bit of a pain and the torch being hot all the time but made out fine with the fixed current.

Greg
 

Robert LaLonde

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#10
Its probably 30+ years ago since this unit was last used. My dad pushed it with an old Hobart DC generator stick welder (I loved that welder for burning rod) that died when I was in my early teens. He didn't seem to be aware you could use it with an AC source either. He has a cracker box almost just like mine except his is older and has a copper wound transformer. Hmmm... I've over 50. I wonder how old this thing is. LOL. The TIG torch has a local (defunct) welding supply house name on it instead of a maker's name, but if I don't like the torch they are easily replaceable. Actually now that I have taken this one apart... they are pretty simple devices. Atleast for an air cooled one.

Got side tracked by customers and running some errands so I probably won't make sparks until tomorrow.
 

Robert LaLonde

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#11
Looks like the unit might have bounced around a bit to much. When I power it up it seems to do nothing. By cranking up the current on the cracker box I was finally able to get an arc by touch starting, but no sign of anything that looked like a high frequency start. I certainly won't be able to weld the thin stuff I was hoping to at twice the current it should be. I guess its time to put the leads back on the cracker box and put it back behind the air compressor.
 

f350ca

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#12
The one I used had a vibrator that Im guessing generated the high frequency. You could hear it hum and see a slight arc off the points. Maybe struck or the points need cleaned.

Greg
 
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