Tack weld with Tig?

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This is probably stupid but how do you make a tack weld with a tig welder?I thought once you start a tig setup its best to keep running your bead
Reply:I do it all the time..Start puddle..Dip..Stay there.. Dip again..Stay there and as you let up on the pedal go around in circles..About the size of the "o" on your keyboard..And slowly pick up the torch all in one motion..Its easy.....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:Depends on what you are tacking together.  Sometimes I won't even use filler for a TIG tack.  Makes it that much easier to run a bead right over the tack later.
Reply:TIG tacking without adding filler (autogeneous) is also real handy for alot of things like thin sheet or wire, as long as the joint fitup is real good (minimal gap).For thin stuff, trying to get a tack weld to bridge a small joint gap is very difficult, as the joint edges melt, surface tension tends to "ball up" the pool and the edges melt back away from each other, rather than coalescing into a single spot.  One fix for this is to quickly dab a bit of wire into the melt, but this is difficult on real thin stuff.This problem can be overcome by using a real quick and real hot "Zap" of current, with the tungsten held extremely close to the joint and pointed equally at both members.  If the tungsten is too far away, the heat is not concentrated enough.Experiment with the amperage setting depending on thickness, but for something like 1/16" sheet,1.  try 150 - 175 amps,2.  stick the tungsten out of the cup so the cup can be rested on the joint and tungsten gap with the root of the joint is about 1/32",3.  start the inert gas flow by hitting the foot control once while holding the torch away from the work, 4.  quickly position the torch and electrode on the joint before the gas post flow stops, 5.  close your eyes and turn your head, 6.  hammer the foot pedal quickly ON/OFF, 7.  open you eyes and take a look at a perfect round tack weld.Adjust the current or the weld time (foot pedal On/Off speed) to control the size of the tack.  Some welders have a built in "spot timer" which is ideal for this tacking.I once had a school assignment to make a model bridge out of 1/16" wire and sheet, and all the tiny joints had to be brazed with oxyacetylene.  I used TIG to tack every joint first, holding the parts in place with one hand, tacking with the other.  When the bridge was all assembled, I dabbed a bit of braze on each joint.  The other students were pulling their hair out.
Reply:Zap's description is a good method to put in a strong tack weld and prevent cracking of the tack.  Thicker metal requires a larger tack, the addition of filler metal, and gradual downslope of current to prevent a crack.A small tack on heavy material is cooled very quickly (quenched) by the surrounding metal which can cause hardening (embrittlement) of the weld and heat affected zone (HAZ), and induce high tensile stress on the weld.So as MAC702 says, a tack without filler is easier to weld over, because you have less material to penetrate and no filler metal bump to smooth out.  Since a tack without filler on heavy material is susceptable to cracking, it is important to fully consume the tack weld so that a residual crack is not left at the root of the weld.  Is some cases, like open root pipe welding, a heavy tack is made with filler, then it is ground (feathered) to reduce the thickness so it can be consumed by the weld.
Reply:If you are making something like say a tank then you may have literally hundreds of mini-tacs holding it together.When I worked in a boat factory I had to tig-tac bunches before we migged the crap out of it.We used nothing but an on-off button and it worked great. Once you get the hang off it it is a good system for welding aluminum. I prefer a fingertip control but on my old air-co they were real bulky so I rigged it with the button and it was like owning a new welder. Just set it a little hot and let off when it starts getting too hot. Lets you make nice welds right up to the end.When I worked in the ambulance factory we used the fingertip control with the remote contactor only  and remote amps turned off (same setting as the button) and made loads of compartments out of treadplate...once again hundreds of mini-tacs with no filler.As for welding without tacking I have certain jobs that I do from time to time that I feel I can do faster and better without tacks but I know exactly how the parts or going to expand and contract and can tell when I'm "losing" it. That comes from losing it and going too far and either scrapping the thing or cutting it apart and doing it over in years past. (that's why it ****es me off when they hire trade school rookies for the same money as old timers..but wait ...thats a different thread...stinkin' alzhiemers)All that said when I tack stuff on the jobs I do nowadays in my shop (or in the field) I do just like Zap said. ...they weld over just fine on aluminum....you may need to feather the ferrous stuff tho..I try to stay away from that ... keeps me "pure" Miller Dynasty 700Miller 350P with Aluma-pro push-pullMiller 280 Dynasty with expansion card Dynasty 200 DXMigMax 215 Enuff power and hand tools to create one of anything..... but mass produce nothing!!!