Technical Difficulties from on Top of the Mountain
2004-04-20
  Melted metal and burnt skin
I really like TIG welding. I started out really hating it, because its probably the worst of all four types of welding in that there are a bunch of different variables to mess with. If you have several of them wrong, there's no simple iterative process of messing with one and seeing improvement. But that's only the half of it. It took like an hour and a half just to get the machine setup right.

This is after reading the manual -- twice.
Now the manual is pretty worthless, but so is the layout of the panel. Tell me if it occurs to you what the settings should be here:


Just so you know I'm just not daft, the shop teacher was dragged into this setup after I had spun my wheels about 10 minutes and we both started taking things apart, checking gas feed lines, cords, switching remote pedals. It was only after my second machine and third petal that I started randomly flipping switches and got the gas to start flowing (ok, so the gas solenoid isn't stuck), and then noticed that the gas shut off after 10-15 seconds. It then occured to me that it was going through its post-flow time (at which point I turned down the post flow knob and hit the pedal again which started the gas and then stopped it after a few seconds).

Now I'm normally pretty quick to debug things (anything from code to car engines). Its just that this time to test it, the machine has to be live, and if you hit the pedal you have 250A at 90V live on the stick (you hope), with the added bonus of high frequency that will allow it to spark out through the air much farther than usual. So I'm a little more cautious and slower to run through tests. For instance I will turn off the machine any time I'm opening up the bottom access panel, taking apart pieces or connecting/disconnecting cables and hoses. I find it amazing that I got the thing to work at all.

So finally I had the machine doing what it was supposed to be doing (I think), then I turned my attention to the TIG gun. Now there are seven pieces that you have to put together on the working end of a TIG gun: the handle, the gaskets, the back cap (stub, short, medium, or long), the collet & collet body (0.020, 0.040, 1/16, 3/32, 1/8, or 5/32), the Alumina Nozzle (1/4, 5/16, 3/8, 7/16, 1/2, 5/8), and the tungsten electrode (pure, 1% or 2% thoriated, ceriated, zirconiated, or lanthanated). They all have to match each other and the job at hand.


A nice illustration, but no--I didn't have water cooling. That's only for the big jobs.

I was going to start with thin sheet metal (ok, 16 gauge is not thin for sheet metal, but its thinner than 1/8" plate), so I wanted a small electrode. I dug through the box and found a ton of 3/32" (pure and 2%), a few 1/8, a box labeled 1/16 but obviously holding 3/32 or larger, and after picking up two dozen pure tungsten electrodes off the floor because their container wasn't shut right, I finally found one box with some actual 1/16" in it. I then dug through the parts for collets and collet bodies that matched and grabbed a #7 nozzle. I took everything over to the welding station and assembled it, but the collet just wasn't grabbing on to the electrode. Hmmm. Back to the box of parts, and this time I assembled my pieces on a spare torch to make sure they worked together. Ok, good. Now back to the welding machine and transfer all the parts. Worked there too. Ok, next I had to pull the electrode back out and go get the grinder.

Welding tips must be properly sized for the job, type of metal, and amount of current. The tip angle will affect how the arc forms, spreads and penetrates, so its good to get it right. And you've got to grind it the right way. You can't grind it from the side (radially) or towards the tip. You've got to run the end longitudinally, head-on to the spinning of the wheel (where it tends to push it back towards you). Also, you want to make sure you're in a weld ventilated area and don't breath any of the dust from grinding--thorium is radioactive. I tended to end up with flat faces on the sides of my tip which gave me some flairing, but I did ok.

There's an entire sub-industry that just makes grinders for tungsten electrodes. These things can run up to several thousand dollars (more than most of the welding machines I've been looking at). Still, if you're doing automated (robotic) TIG tube of pipe welding, you need repeatability in your tip preparation, so I suppose there's a use for these.

So after running line after line, and making a mess but not really a good weld, I'd show it to the teacher and he'd suggest that I turn up the gas flow, or switch tip sizes, or turn down the power, or go slower. Finally he came over and watched, fiddled with the knobs and make suggestions, but we still weren't quite there; so he took the torch himself and ran it a bunch until he finally got a decent result and then said, "There. Use those settings." So I got about an hour of real TIG welding in. Then right before class was over I pulled out some quarter inch plate squares I got at the scrap yard and started working on a cube. Doing thicker stuff is actually easier than the thin stuff. The tip doesn't need to be as pointed and you just crank the amperage way up. Doing corner welds doesn't have to have filler so I was just ripping along, melting the two edges of 1/4" plates till they merged together. Great fun, but I ran out of time before I finished so I'll have to work on it some more next week.

My final mistake wasn't apparent until the next day when my wife asked me if I had been out in the sun. Since I normally hide all day in the basement, it is rare that I get any sun at all. My skin complection is usually closer to albino troll, but today I had a bright red spot on my neck. I had just purchased a new helmet, since I had figured out that I didn't need an auto-shade which are very expensive anyways. What I really needed was something that was light and that I could adjust to flip down easily, so when I was at the welding shop I asked them for the lightest helmet they had and got that along with some gloves that were too thin and some thin 0.023" wire for the MIG welder (which I didn't get around to trying). Well, since I hadn't broken in my helmet completely, it didn't always flip down all the way and I ended up frying a two inch patch around the collar of my shirt. The stinging should stop by next week, but hopefully I'll remember to button up my jacket up all the way to the top and flip the helmet all the way down before welding.

[links]
An introduction to TIG welding.
How to prepare tungsten electrodes.
TIG torch parts from Mister TIG.

 
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