Hi there,
I do a lot of TIG welding and maybe can help a little..
I weld mostly Stainless and Aluminium, no basic steels, but do a lot of Moly based tubing for motorcycle frames ( off-road stuff)
Features I consider essential are
foot control of amperage:
especially on thin materials, more especially on aluminium – you need to be able to inject hi amps to heat the base material up and reduce as you weld. If your welder is capable of pulse control, you can use that to make nice scalloped welds, if not, active pedalling on the foot control – Dab the pedal, heat the material, pull torch back on the weld, apply filler, back-off on the pedal, move forward along the weld and repeat…you get into the groove after a while and it flows..
A GOOD fast response welding helmet,
( not the old dark glass flop around jobs) The darken response time must be reliably rapid, and you must be able to set the opacity since the weld 'brightness' varies a lot at the different amperages used for different thickness materials.
High-Frequency/Voltage arc start:
Not 'essential' but makes life much more pleasant. Scratch start works fine, but use a piece of pure copper sheet next to the weld to start the arc on, and then walk the arc to the weld. Not nice if you are not proficient, since you WILL many times touch the weld with the torch tip, and then it's clean/regrind the tip, and then scratch start, etc..Some welds are at angles where the copper start strip is awkward, and so you start the arc on the base material, contaminating the tip and subsequent welds..
Some of the cheaper systems without foot control but with HF start supply a torch with a finger activated HF start mode. This works, but your hand suffers badly! the finger is always poised over that button and the rest of the digits take big strain handling and manipulating the torch – Don't go there!
Automatic on/off shield gas control:
Some cheaper systems provide a torch with a finger controlled valve on the torch to active gas flow – Don't go there – it just detracts from the dexterity needed to control the torch.
Torch Size:
A small torch with bent head is nice,neat, zippy, gets in places, but weld for 20minutes on 10 minutes off at 200 amps and you will be wrapping the torch in wet rags to cool it…
I have three torches, two that are 'T' shaped, one large using 2.4 and 3.5mm Tungstens, one medium in which I use 1.2mm up to 2.2mm tungstens, and a small pencil shaped torch for 1mm up to 1.6mm tungstens – the later torch normally used on material that require up to 30amps max ( 0.3 to 1mm S/Steel, for example)
Tungstens:
2% Thoriated for S'Steel and Moly ( sure all the OHS folk will jump in here and swamp us with safety issues..you must grind it wet only, you must grind it outside, you must grind it while in a full HazMat suit, blah, blah..)
Ceriated or Lanthanated (grey band or Gold Band resp.) for Aluminium ( and AC of course).
Other Issues:
You say 'thick and thin tubes' – what do you mean? To butt weld two Aluminium plates of 10mm each you need a solid 200amps..or you have to pre-heat the entire assembly first, and hope you get good penetration at 150amps..I normally set my machine to 100amps for 2mm Ali, 150amps for 6mm, and 240amp for 10 to 12mm, and then use the foot control to get what I want.
I am assuming from you opening statement that you have not Tig welded yet – if I am wrong, forgive me and ignore most of this post…Tig welding is as much an art as a process, requires good eysight to judge arc length, which must be kept as short as possible, more so the thinner the materials, a really steady pair of hands so you don't stuff the tip into the weld, or the rod into the tip, etc.
And then , practice,Practice,PRActice, PRACTICE……
To get the foot synchronized with the torch movement, and the feed rod synced with the torch motion, and the head flip to get the helmet down when ready..
What else??
Joe