Thread: TIG amps question

This is an interesting thread!
Could you use ordinary house rockwool or fibreglass bats - maybe cut into strips?

Originally Posted by Legion

Today I watched Jody's most recent video. At the ~11:30 mark he is welding a 1/4" steel outside corner. I would be cranking my dynasty 200 right up for that but he says he's set to 120A. The resulting weld looks fine and the weld width seems perfect, from corner to corner. Why would he go so low? I think I would feel like I'm just washing heat in slowly and not getting penetration and be more likely to try 180A->200A. Is it because it's an outside corner so the root is thin and he's digging right in there? Still seems low to me. I guess I haven't really done much outside corner stuff and when I have I feather and it's generally a low setting anyway (all I've done is outside corners of mitred corners on frames with ~3mm or less material and some tube and pipe caps with imperfect fit up).

A non-related question that I was thinking of today - insulation wrap - what does everyone use for slow cooling of thick pieces? Anything cheap and accessible to a backyarder? New trailer or two next year and I might build my own suspension where some parts are thick and could possibly benefit from a bit of pre heating and slow cooling. Some 8-10mm brackets and things. Things that are difficult to pack in sand where I'd prefer a wide reusuable tape or something.

Using the 1A/thou rule becomes less accurate as thicknesses increase. For example, amperage required for an open root joint will be affected by root gap and root face dimensions.
Experienced welders will generally set a machine to give the arc conditions that they want, rather than an arbitrary figure. Jody would be observing the way the weld washes in, the tendency to undercut and several other factors. You would have noticed yourself that sometimes you hit a set of parameters that are just sweet to weld with, they wash in nicely with no undercut and the rate of travel is such that you do not feel rushed or stressed while welding. Jody may have a preference for welding a little slower than you would at 2-250A.
To answer your second question, there is no need to do anything other than air cool mild steel and even some of the more exotic materials.
Mild steel with a carbon content of less than .3% will suffer no ill effects from air cooling, (theoretically even water quenching should not make much difference, but I still wouldn't). Likewise there is absolutely no need to preheat those thicknesses of section in any of the materials likely to be encountered when trailer building. In fabrication terms 8, 10 or even 12mm are not really considered thick.
How are you planning on welding these, stick, MIG or TIG?

I tig everything, even when it's wildly inappropriate . I still have the little Kemppi stick welder and the dynasty obviously does stick but I have been 100% tig for some time. I prefer the infinite control in all positions. Production speed is obviously not an issue for me.

I have access to a decent mig but no experience or interest.

I'm thinking of a beam axle with multi links and coils or bags and shocks. My trailer supplier mentions pre and post heat for axle welding without being specific. I would minimise axle welding through design but some would no doubt be required. I'm not as concerned with bracketry where I can prototype and redo in the unlikely event I stuff up but with axles I want to be prepared to minimise the chance of warping or cracking welds.

Axles will probably be in the 50mm/2 tonne class.

I might do a lighter trailer first which would be a good prototype. I've been told we need a new skiff trailer, so in the 300-400kg aggregate class. After that I'd have a good idea for the (hopefully) <1.5 tonne off-road camper.

My guess is that the preheat mentioned was relating to the 45mm solid axle.
A 50 degree preheat would most probably be all that was required, just nice and warm to the touch.
Given that you like tigging so much, there will be nothing to stop you tigging where ever you like on the suspension. Most would choose other options due to speed/convenience.

I watched that video - Jody did seem to be progressing pretty slow with that weld - maybe he knocks down the amps and slows things down just to make sure he gets some good steady footage? The guy really is a legend - just for putting out a pretty decent video every week. BTW if you haven't got some already, his TigFingers are actually pretty good.

Legion, I know what you're saying - if you haven't got enough amps it's frustrating and unsatisfactory - but it's pretty easy to tell when you're not hot enough as well and there didn't seem to be anything wrong with Jody's weld (a bit under-filled maybe??). I would've been looking at around 140 amps but I'm not sure - can't tell without actually doing it. Normally on something like that I'd put the machine on something like 150 and then just foot pedal it to what worked. Like you said - just stand on the pedal to get a good puddle then back off when it gets going. If the puddle didn't form straight away I'd go back to the machine and crank it up a bit. I wouldn't be quick enough to keep it under control at a straight 180-200 amps - that seems high to me.

Thanks for the input Mick. I guess there's no better way to find out than to have a shot. I've got some scrap 8-10mm lying around so I might try and see what settings work for me.

OK, had a shot today. 6mm material, so right in line with Jody's 1/4".

2.4mm 2% lanthanated
120A
no pulse or anything
Probably 7 or 8 Lpm
6mm mild steel scrap, ~100mm x 40mm
2.4mm ER70S-6

Now before you all laugh, I don't have a bench. Normally I use jigs and things or the job to rest on but this time I just laid it on a frame I'm making and clamped the pieces to some 30mm SHS so I freehanded the torch and the filler and I was all over the place. I'm not particularly steady.

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I didn't dip but that's about all I did right. The pieces were curved apart at one end so there was a root gap at the beginning. You can tell how big because I didn't start right at the corner. As a result I panicked and went too fast and you can see I didn't fill the fillet. I still had a bit of material through the back of the root for the first 10-15mm from the gap, as you'd expect. Later on a couple of wonky bits but it's OK for me for freehand. Excuse the start and end, I didn't really care for this test piece. The weld is a bit concave in parts. I would prefer to use 3.2mm or 4.8mm filler but 2.4mm was the biggest I've got.

I cut it in a couple of places and thought I'd try and etch it. Unfortunately the only two pieces of sandpaper I had were 125 grit and "medium" and I was lazy so I didn't effectively polish it at all. And I had nothing suitable to etch with so I tried soaking it in bicarb for an hour or so but it didn't show up much. Penetration wasn't as much as I'd like and it's hard to see. The curved sides, basically it's done the reverse of that, penetrated in to the parent that much. But I made three cuts and the root was nicely filled in all three so I'm happy with that.

So I guess Jody knew what he was doing. If I had to do more I'd probably bump it up 10A and use much bigger filler and see how I went.

Comments and criticism welcome.

Well I don't reckon it would come apart too easily but for an off-road trailer I wouldn't be happy. But then again you'd have a gusset or three anyway with that sort of joint. A few other comments:

• I try and treat my test pieces like the real thing, so I clean them down, try and get fit up right etc. so any deficiencies aren't 'just because it's a test piece'. It's tempting to do a rough practice - but all you're doing is practicing being rough.
• the root gap wasn't really needed - the amps should be enough to get right down in the fillet and ideally add just a tiny bit of fill on the inside of the joint.
• if you only have 2.4mm filler, then either feed 2 filler rods held together at once (trickier than it sounds - I'm not really recommending this), or just do 2 passes (recommended). For this, just do a nice root weld concentrating on getting the penetration right through, but not too much. And then a second pass adding lots of filler to round out the corner and at the same time make sure you're including the straight edges into the weld. Your weld is under-filled.
• if you haven't got a bench, clamp your angle iron to a fence or something at comfortable/stable height. Your welding looks pretty neat though really - considering.
• at the start of the weld you can weave the arc up the side a bit, add filler to fill the gap in the middle, then quickly move the arc across the gap to the other side, add filler in the middle again. So your arc is concentrated on the parent metal (not burning a big hole in the gap), but you're adding filler into the gap.
• If this was at 120 amps, then I think that was about the right current for the first pass with 2.4mm filler. If you had thicker filler and doing it in one pass, then probably 140 amps would be as much as you'd want.

If this is the first thicker piece you've tried then I think you've done a pretty good job.
Cheers
- Mick

The root gap was only from the start to about the first hole. Maybe the pieces were cut with a guillotine or something and they weren't straight. Fit up was perfect for the rest.

I would have done another pass but I just wanted to answer my own question about amps and it kind of did that.

Some great suggestions. I will be doing more welding tomorrow so might try another test bearing them in mind.

The most important thing I got from your post was not to pissfart around. I'll remember that. I just grabbed some rusty, millscaled pieces, flap wheeled them and went for it. No dry runs, no hand steady rest, crappy start and finish. With my hands shaking around in mid air I'm mostly worried about dipping whereas normally I position myself so I can relax and just watch the puddle.

It actually looks much worse than it is. The beginning was certainly underfilled but after that it's mostly "almost OK". The cross section was randomly chosen, not trying to pick a good or bad spot, and that one was probably near those first few dots of silicon. The other cross sections were similar. The camera angle makes the weld look quite concave but really the last 2/3 was OK. Yes, another pass would make it better though.

Given I normally do thin stuff in a single pass, for something like this would you weave the second? Never had to do that but I can't see the arc being wide enough to cover the whole throat on the second without weaving. Dabbing at both sides of the weave?

OK, another test piece.

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^ The black dot at the end is silicon catching the light, not void.

IMG_3021.jpg

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^ Silicon again.

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^ Not happy about the extra filler in the middle but not enough to justify trying to wash it away or another full pass. I'm not sure why that ended up there but it's obviously from a restart. For some reason my hands were shaking like crazy today despite a wrist rest. Maybe because I did a bunch of exercise yesterday and I was welding at almost shoulder height so I was holding up most of my arm before my wrist.

Settings all the same as yesterday. 120A, three passes but not waiting for it to cool so the second and third were already hot.

One question that can be seen in the last photo - the pieces were unequal length. I went right to the end of the join but should I try to fill in the ends so that you can draw a line from the longer piece to the shorter? You can see the remnants of the face of the longer piece in that last photo.

I found some old oven cleaner so I tried another random etch.

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My highly technical polishing regime was to use a flap disc, probably 60 grit.

I'm not sure why, but I think the etch is showing the last pass only. Does that make sense? Because it's pretty much outside the boundaries of the parent metal and if that were the case there would be huge voids, zero fusion, and it would fall apart in your hand.

That's a shame because I would have liked to see the total weld definition, not just the last pass.

Originally Posted by Legion

IMG_3023.jpg

One question that can be seen in the last photo - the pieces were unequal length. I went right to the end of the join but should I try to fill in the ends so that you can draw a line from the longer piece to the shorter? You can see the remnants of the face of the longer piece in that last photo.

Hey Legion - first thing is - good on you for going through this exercise - many wouldn't.
Regarding your question, I don't quite follow what you're asking - is it whether to make a smooth transition between the left hand faces of the two pieces? Personally I would, but it probably doesn't matter a whole heap.

With the little restart bump - when you restart, back the arc up over the last puddle, without adding filler - so in effect you are replicating the last puddle before you stopped, then continue on as normal.
Looks pretty good to me though.

Originally Posted by Legion

That's a shame because I would have liked to see the total weld definition, not just the last pass.

With your etching, I've used oven cleaner before and it seemed to work pretty well. I'm not quite sure what's going on with the invisible first pass.
In both photos, particularly the first one you can see a little section of the edge right on the inside of the fillet that hasn't been included in the weld - this is an area for a crack to develop from. Much better if you can get the penetration of that first pass to get right through - like the keyhole effect that Jody talks about in his videos.

Yep. The longer piece there at the start is maybe 2-3mm longer so I have a discontinuity. I was wondering if I should try to make it a smooth edge between the pieces. So at the moment you could draw a straight line along the shorter piece onto the longer piece but I felt like I should have made it diagonal so it's a smooth join.

As to weaving, I didn't need to. There was enough heat to wash in the edges with just a few millimetres weave. The shaky hands were probably enough . I filled on the first run, filled (less) on the second only having to dab in the middle as required and just washed in the third with no filler to make sure I ate into the toes nicely. Probably could have added a few dabs but it's already smooth and convex.