Question from a New TIG learner

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I am just learning Tig using scratch start Tig with a DC machine.I am seeing a pattern in my Tig welds that I do not like and it is where I end the weld by breaking the arc. If I weld from end to end or if I weld from each end to the middle I see the same result.I get a pin hole (or larger) in the weld whenever I stop.  It seems like an impurity (air) gets in the weld in the portion of time from me breaking the arc and getting the argon gas back on the weld as it cools.  As folks have gotten scratch tig welds to pass certification there has to be a way to not have it happen.  I guess it take more practice and some technique/skill that I do not yet have.  I know there is a lot of experience and folks that do cert scratch start Tig on here so I am looking for suggestions as to how to better my technique and specifically how to avoid the end of weld issue.  Below are some pictures showing the issue and what I am talking about.
Reply:That is called a crater.  It is because you don't have the ability to taper your heat off slowly as you close the weld. To prevent the crater you have to taper your heat off slowly and add a little extra filler as you end the weld then continue shielding the weld with argon for several seconds after the arc is out.  You are in the same boat as me using this type of primitive Tig. To extinguish your arc you have to flick the torch off the work in order to kill the arc then quickly get the torch nozzle back over the weld to try to shield the end of the bead.  By then, it is too late and you get a crater.I have occasionally managed to prevent the crater by backing up the arc just a little away from the end of the weld, swirl the torch in small circles around the puddle and add one dab of extra filler as you do so.  Flick the arc out and then very quickly get the gas flow back onto the weld bead.I too would love to hear what the really good tig welders do in such a situation with this type of tig welding.I recently bought a Miller HF251D-1 arc starter box at a great price and I no longer have to scratch start and I have 15 second post flow timer.  Still, I have no way to extinguish my arc without having to flick the torch off the work when I am finished with the bead.
Reply:With a joint like that, weld to the center from both sides. When you are ready to end the weld you need to speed up travel speed until there is no more puddle, just the arc moving along the steel. When the puddle has "Dried up" you can break the arc and then get shielding gas back over the end.Airco Ac/Dc 300 HeliwelderMillerMatic 200 (stolen)Miller Maxstar 150STLMiller AEAD200LE (welding and generating power) Hobart MIG
Reply:Originally Posted by SquirmyPugWith a joint like that, weld to the center from both sides. When you are ready to end the weld you need to speed up travel speed until there is no more puddle, just the arc moving along the steel. When the puddle has "Dried up" you can break the arc and then get shielding gas back over the end.
Reply:Originally Posted by MWaldenCan that same "speed up" technique be used if you cant weld from ends to center and need to stop the weld at the ends?  Maybe back up with the arc and increase travel till the puddle dries up as you said?
Reply:On something that needs to be welded to the end with a nice bead, you can use run-off and run-on tabs and just zip them off when done.I've used them on spool gun aluminum and SMAW, but the same would work for tig.SquirmyPug's method is likely less hassle though Dave J.Last edited by MinnesotaDave; 07-30-2013 at 09:47 PM.Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:I knew I saw this done on a video..Watch near 7:30 to see how to snap out of the weld.Airco Ac/Dc 300 HeliwelderMillerMatic 200 (stolen)Miller Maxstar 150STLMiller AEAD200LE (welding and generating power) Hobart MIG
Reply:Well damn!  The one video of Jody's, that I dismissed, was this one!   I figured since it was sanitary tubing I wouldn't need to see it.  That will learn me dern me!
Reply:That foot switch cutout seems like a really nice idea for stopping the arc without flipping the torch head out and back.
Reply:Originally Posted by pineThat foot switch cutout seems like a really nice idea for stopping the arc without flipping the torch head out and back.
Reply:Originally Posted by MWaldenIn my case that switch would be carrying 240v and I believe Jody's is as well.Could this same style switch not be used to interrupt the ground cable instead?  Would that not also do the same thing yet not have 240v under your toes?
Reply:He was cutting the weld lead with that wooden foot switch thing.  He had the rod holder clipped to it.He was not cutting power to the welder.Dave J.Last edited by MinnesotaDave; 07-31-2013 at 12:35 AM.Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:That is what I thought.
Reply:Pretty darned good idea I think.  I have the exact same switch on the battery in my tractor - they are cheap Dave J.Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:Originally Posted by MinnesotaDaveHe was cutting the weld lead with that wooden foot switch thing.  He had the rod holder clipped to it.He was not cutting power to the welder.Dave J.
Reply:When I use scratch start, I have a piece of copper. It an old heatsink from an Intel XEON processor. http://imgur.com/ldgnueEJust pull off the fins and take the screws out.  Lay the copper piece at the spot where you want your weld to end. Lay the bead as normal, and as you get near the end, just move the arc onto the copper, then snap off. No crater or porosity.
Reply:Originally Posted by joeftw18When I use scratch start, I have a piece of copper. It an old heatsink from an Intel XEON processor. http://imgur.com/ldgnueEJust pull off the fins and take the screws out.  Lay the copper piece at the spot where you want your weld to end. Lay the bead as normal, and as you get near the end, just move the arc onto the copper, then snap off. No crater or porosity.
Reply:Originally Posted by MWaldenAnother good idea as long as long as you are welding horizontal.
Reply:I work in the refineries and we don't have access to fancy switches lol.  all the guys do is just speed up and snap off, poof no crater
Reply:Since this thread is about craters I thought I would put these in here.  I used the trailing out tips I was given here and got better results.Some were trailed forward and lifted till the arc went out and others I backed the torch up and trailed off.
Reply:Break the arc up on the filler wire or up on the bevel.