How large of a gap when starting a TIG arc?

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I've been having issues starting the arc when TIG welding using an old Airco 300 AC/DC machine. It has a starting current control (ramps up and back down in 2/3 of a second) as well as a high frequency intensity control. With properly sharpened tungsten (2% thoriated) and plain steel, I frequently have to get the tip very close, probably around 1/16" away from the steel before the arc will start. This also means I'm touching the tip to the work much more often than I should. Once the arc is established, I can pull back to 1/8" or more and weld just fine. For you guys with experience with the older TIG machines, how far will the arc initially jump?
Reply:I'm NOT an expert on this (tig) , but, it sounds like maybe you need to file(sand) the points for the Hi-Freq  and re-gap them. I've never had to do it to my  miller Dial-Arc 250 H F , but that's  because I don't use it much ( very seldom ) .[SIZE="5"Yardbird"
Reply:I don't have an old TIG machine, but I have noticed from time to time the tip of the tungsten looks perfect but I have trouble stating an arc after use.  All I do it a quick scrape of the tip on the table and it removed what ever was there and the arc starts right away.Maybe some junk on the tungsten tip unless it is a fresh grind then it should start with no problems.Build a Barstool Racer at BarFlyRacers.com!
Reply:I notice on my machine that if the gas is not turned on the arc will not start either..Sometimes at start up there is no gas in the 25 feet of hose to the torch..I ususlly hit the pedal and let the hissing start before starting..Other than that no problems.....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Sometimes it helps to let off the pedal all the way, ground out the tungsten, and the start again.  I've noticed that on a couple of machines.  I assume it helps discharge a partially charged capacitor it the starting circuit and it usually works for me.
Reply:possibly not a very good ground?6G zirconium 702 GTAW 2" xxheavy6G P.E.D. carbon steel GTAW 2" xxheavy3G titanium Gr. 2 - Gr. 7 GTAW up to 3/4" 3G 316L stainless GTAW up to 1" 3G carbon steel GTAW up to 1" 3G Hastalloy GTAW up to 3/4"1G tantalum GTAW up to .060"
Reply:The gas solenoid on this machine leaks, so some argon flows whenever the bottle is open (yeah...wasting gas). With the starting circuit that kicks out more current at the start of the weld, touching the tungsten to the metal usually causes it to stick when depressing the pedal.I found the manual for the Miller version of this machine and will give the spark gap a check.
Reply:I guess what I'm asking is with a properly set up machine, how big of a gap should the arc be able to start across initially, regardless of what kind of TIG machine it is?
Reply:The arc should start with the same gap you are welding with. I have found that sometimes when the arc wont start. All I do is touch the tungsten to the work lift it, then hit the pedal, and get an instant arc. My little tig did the same thing ocassionaly. It might be the tungstens. Ceriated seemed to do this the worst. Sometimes the arc would not start until I reground the tung. I mostly use lanthanated and some thoriated and starting is not a problem. Seems to be with ceriated.mm135HTP Invertig 201 With water cooler9" Southbend LatheLots of hand tools.
Reply:Although usually not the most desirable start, I would say that the HF should be able to start the arc at at least 1/2". I have seen arcs started from an inch or two ayway. The hf arc usually goes about twice as far.be careful, don't get shockedand a long arc can leave ugly pecker tracks on your base metal.Last edited by Mark...; 02-23-2008 at 04:01 PM.
Reply:Playing around today I got it to about 2"..Was rather easy also.....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Back when I used the tig quite a bit and had HF and a foot controller I used about 1/4" to start and never had any problems. It was a 400 amp machine and that's a lot of oomph.The difference between art and craft is the quality of the workmanship. I am an artist.
Reply:I just cranked the high frequency intensity from 70% up to 90% and that helped a lot. I just don't like running anything flat out like that.