question about scratch start tig

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I fired up my OLD pre 1970 welder to try some Tig now that I have 100% argon.  This wasmy first try at scratch starting (couldn't find any carbon to start on...)  and I havn't tig'edin allmost 2 years so I am pretty out of practice.  After 3 or 4 beads playing with the current and gas flow I got it working OK .    The only strange part is when I reached the end of the cupon where I had tacked it - and wanted to stop the arc - I pulled the torch back to do so.  But I could see at I started moving the tungsten away the puddle blewup like a bubble and then burst at the top leaving most of the body of the bubble intact.On the last one I did the bubble collapsed back down but you can see a definate "funny" snout there.  What is the correct way to stop the weld and get a normal looking termination ?1/8 plain steel, 1/16 2% thor. electrode, about 30 amps ac 60 hz. (beveled edges to about 1/2 the thickness of material),  small cup - no G.L.PS- just wanted to get some practice before I get the dynasty !TimLast edited by jethro; 11-30-2010 at 01:43 AM.
Reply:- I pulled the torch back to do so.  But I could see at I started moving the tungsten away the puddle blewup like a bubble and then burst at the top leaving most of the body of the bubble intact.On the last one I did the bubble collapsed back down but you can see a definate "funny" snout there.  What is the correct way to stop the weld and get a normal looking termination ?1/8 plain steel, 1/16 2% thor. electrode, about 30 amps ac 60 hz.PS- just wanted to get some practice before I get the dynasty !Tim[/QUOTE]When you pulled the torch back, the weld puddle lost it's Argon shielding, and the resulting bubble occurred.I welded boiler tubes for many years using the scratch start method, and to end the weld,you would stop feeding rod and speed up your travel. The puddle size would diminish, and the torch was turned up and away from your work, and the arc was broken. This was all code work, and we would take the rotary file and touch up any irregularities. We got pretty good at making clean breaks using this method. If you have a remote control, use it to slowly turn down the amperage at the end of the weld bead. I would have it handy, and after the weld was completed, would lay down the filler rod, and turn down the amperage.Quite often we had an apprentice working with us, and they would man the remote, using voice commands from the welder. Whatever works!Bgbkwndo.
Reply:I can see how that might work great when you are going arround a pipe joint where you can do a long  tapered overlap with no rod and the current decreasing. ( If I understand your senario corectly)I am just practiceing on 1 by 3 inch cupons - I run out of material at the end.  Do I just slide a sacrificial piece up to the end and go on thatto end?This thing has no means for remote current control.  Just a big-ole variable transformer.So is it the oxygen interacting with the puddle what causes the puddle to inflate ?Last edited by jethro; 11-30-2010 at 01:45 AM.
Reply:Quickly snap the torch 90 degrees to break the arc then quickly return the torch over the work for some post flow argon shielding. Thats what I do. You have to keep the torch close to the work while breaking the arc so you can keep your argon shielding there while the puddle is still molton.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:What snoeproe said.  If it's a groove weld, you'll want to terminate your arc on the sidewall when possible also.
Reply:For what its worth, I support what Snoproe and Supe have said.
Reply:Originally Posted by Bgbkwndo- I pulled the torch back to do so.  But I could see at I started moving the tungsten away the puddle blewup like a bubble and then burst at the top leaving most of the body of the bubble intact.On the last one I did the bubble collapsed back down but you can see a definate "funny" snout there.  What is the correct way to stop the weld and get a normal looking termination ?1/8 plain steel, 1/16 2% thor. electrode, about 30 amps ac 60 hz.PS- just wanted to get some practice before I get the dynasty !Tim
Reply:OK, I will try these methods for stopping the arc without a bubble....ThanksT
Reply:i hear you guys saying rotate the torch to break the arc and then bring it back to resume the gas shield. this clearly interrupts the gas shield for a moment. why wouldnt you pull away to break the arc but keep the gas flow pointing at the   hot bead ? why the rotation..?
Reply:Because it's faster and less turbulent to snap the wrist than it is to try and pull the torch back, which will likely result in long arcing and a small cluster of porosity.  Although you've interrupted the gas shield for a split second, the density of argon should allow it to linger in the weld area momentarily.
Reply:Originally Posted by SupeBecause it's faster and less turbulent to snap the wrist than it is to try and pull the torch back, which will likely result in long arcing and a small cluster of porosity.  Although you've interrupted the gas shield for a split second, the density of argon should allow it to linger in the weld area momentarily.
Reply:YupJust pulling the torch back will not break the arc, it will create a long arc and increase voltage.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720