Tig welding .... single pass & multi pass

Discussion in 'Shop - Fabrication' started by motoxscott, Aug 12, 2008.

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  1. motoxscott

    motoxscott Well-Known Member

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    Here we can discuss the two methods of TIG welding.
  2. fishd00d

    fishd00d What A Joke

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    May 9, 2001
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    San Marcos, CA
    gonna need lots of popcorn for this one!
  3. goofballracer

    goofballracer PAT DAILEY #1 FAN

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    san marcos ca.
    I like double pass cause if the first pass isnt so pretty double pass will clean it up a bit

    just my .02
  4. motoxscott

    motoxscott Well-Known Member

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    I would personally like to hear Derek's thoughts on the matter.

    - Scott @ Camburg
  5. goofballracer

    goofballracer PAT DAILEY #1 FAN

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    Dump?
  6. Chase 2

    Chase 2 Well-Known Member

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    Seriously, why do it at all?

    I'm not buying your heat argument, mulit cold passes vs one good pass. Look at the pics of Dumps work, look at the size of the heat affected area, it ain't that big.

    You mentioned the TIG process being developed for air craft industry, yes it was but, I'm pretty sure it was developed for aluminum. At the time what we now call TIG (then called Heli-arc due to the use of helium as shielding gas) was being developed, the industry standard method for joining 4130 airframe tubing was plain old simple gas welding! AND that was without PWHT (that's post weld heat treating for you non-welders), and you want to talk about heat affected area? You want to talk about aircraft safety? Sorry kids, it all sounds like some guy who drives a desk put a spin on it for marketing to me.

    Many times this weave people are doing is much wider of a weld than needed. For 10 extra bonus points, would some one else please inform the general public what the Welding Industry Standards aspect ratio for the height and width of the fillet as compared to the base metal should typically be?

    The multi pass weld has it's place in heavy, thick material where the material is beveled prior to the joint being welded. But people, you not dealing with those thicknesses in the off road industry. Your waisting your time and money with a technique used by slackards to cover cr@ppy work.

    Oh and by the way the welding industry no longer calls it TIG, (just like they no longer call it Heli-arc) its now called GTAW thats Gas Tungsten Arc Welding.
    Last edited: Aug 12, 2008
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  7. Jerry Zaiden

    Jerry Zaiden Well-Known Member

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    This is where I think you don't get it. The first pass is a very hot little rod almost fusion weld connecting the ID wall of the tube. The second pass is for filler material and the third is to finish filling and making sure the puddle is not undercutting the material.

    Now go look at the process for welding nuclear tube or welding tube for the oil industry. I think after you do this research you will change your mind.

    The top welders in this industry weld Robby's stuff. They are both from the Nuclear world and there welds and technique and bar-none. Both use the weave pattern and it is not for the look.
  8. movindirt

    movindirt Wham Spore

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    Did not the use of gas welding effectively do the job of PWHT? The greater the heat effected area the larger heat gradient. This does not leave a sharp change as would a small heat effected area and why PWHT should be done on welds of 4130 with small heat effected area. Correct?
  9. CRAIG_HALL

    CRAIG_HALL Well-Known Member

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    I'm sure most industrial pipe work welding is over 1/4" thick(oil & nuclear industry) and requires multipass welding, not necessarily a weave...I'm sure when the're weldind thineer material it's not as common. of course if we used a 1/4" tungsten and equal size rod you may be able to do a single pass.
  10. partybarge_pilot

    partybarge_pilot Well-Known Member

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    All the stainless tube I have welded in fuel farms has been single pass.

    Since I'm going for My weld test at San Onofrie tomorrow, I'll let you know. From what I hear, the fab shop is full of old race car builders.

    I personally don't really have a preference as done properly both will work. The weave just takes longer and only happens if someone is paying for it.
  11. Chase 2

    Chase 2 Well-Known Member

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    I totally get it, I've done plenty of multi pass welds on stainless steel pipe up to 6" in diameter.

    So you are telling me that your welder (I'm now assuming that Jerry is not a welder by trade) first comes through with a pass purposefully not adding a "typical" amount of rod, in an attempt to gain additional penetration? You realized that any welder worth his certs should be able to gain the same penetration (if not better) using more rod don't you?

    Jerry, have you ever herd of pushing a puddle by developing something that is called a key hole? Or perhaps you should ask your welder if he learned the technique in school. It's where you obtain 100% penetration, commonly done on aluminum and stainless steel. Basically you get the puddle so hot the back side of the puddle blows out, leaving a "key hole shaped hole in the joint, and then you add rod to the back side of the puddle behind or to the side of the tungsten. When properly done you can't tell which side of the weld is top or bottom as you have developed an equal sized fillet on both sides of the base metal.

    So why is your welder not using more rod on the root pass? Really, I'd love to hear the technical reason. I expect the reason is because he doesn't need too, because he knows he's going to revisit the weld two more times before he's done.

    So after the "root" pass your welder goes back over the initial weld adding a whole bunch of filler rod to build the fillet, he doesn't need to worry about penetration because his "almost fusion weld" has done that, right?

    Now, after adding a bunch of rod on his previous pass, your welder then makes his third pass smoothing out all of the underlaying welds blending it all in with the edges so none of the evil undercut remains.

    To me, even if we were all were to buy in to what you think is so correct, a competent welder should be able to do this in two passes. Simply "burn a root" and then wash over it to clean it up, both passes would simply be using a bit more rod than your technique right? And it would be done in at least one third the time!!! I mean really, if what we know can be done in one pass, and what looks like (by your explanation) could be done in two passes, what's up with the third pass?
  12. Scott_F

    Scott_F Active Member

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    I'll HAZard a guess at 1.5:1. Some of the pretty weaves I have seen remind me of how they used to braze bicycle frames in the old days. I imagine with brazing you need all the surface area you can get.

  13. Chase 2

    Chase 2 Well-Known Member

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    :D Bingo!! And it is the sharp edge that GTAW is know for and in many cases makes it the method of choice. But, if the heat affected area is that big a deal to these guys, why aren't they firing up a rose bud and doing some sort of a PWHT, it sure would be faster and offer a larger transition area than what they are selling.
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  14. J.JOHNSON

    J.JOHNSON Member

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    I think the cats got his tongue now.lol
  15. FISHMOUTH FABWORKS

    FISHMOUTH FABWORKS New Member

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    Most of the Tig welds I see these days lack any sort of crown.There are to many pedal pulsers and people with machines that shouldn't have one.I blame Tv shows for this.ANY ONE is a fabricator these days.

    I don't understand the fuseing the tube part.We only fuse sheet metal thinner then .060.Your welder should be able to weld .120 wall tube in one pass. I use 1/8 tungsten and 3/32 rod around 150 amps. works just fine. If its that inportant then your welder should be making a root pass on the tube first. Just as Chase 2 said "the keyhole". would you then chamfer the tube and put a .030" gap in the joint? make the first pass and then go over with a wash? I still dont see a reason for a wash on .120 wall tube.
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  16. BajaFand

    BajaFand Well-Known Member

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    FYI it was asked in the other thread who did the weave welding on the picture of Robby's truck and it was Ron Stockwell. He also did Chet's truck and both the Hummer's as well as the Stock Full and Class 3 we used to race and Johnny Kaiser's stuff as well. I know he has done welding for way more guys than I just mentioned but I couldn't name them all. If I remember correctly when Ron did our cars he only did the second pass on everything. Scotty who was doing the fabrication work would do the root pass on the whole car (which was a very nice pass) then Ron would come in and do the second pass on everything.
  17. DUMP!

    DUMP! Active Member

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    That's not 100% true. While Ron did do quite a bit of the second pass welding there were actually 4 or 5 people that also were capable and did contribute to the second pass welding on the RG cars you mentioned. The others would be Dave (Guido) Schell, Chris Smith, Donny Gerraro (who still works for RG) and myself.

    Dump
  18. Jkrell

    Jkrell Active Member

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    Location:
    so cal
    I'll take zero credit for the tig on that truck but I did lay down some fine example of the "Mig Weave" on that rig....Its the required technique when scabbing together 1/2 - 3/4" gapped body mounts 24 hours before the baja. Double and tripple passes required to build up material. I'll be happy to share the technique if anybody is interested...:D
  19. Samco Fab

    Samco Fab Well-Known Member

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    Location:
    Reno NV
    Somebody mentions "pedal pulsers" and hints that these people are evil scum wana be fab guys:D

    I add a little throttle when I dip my filler rod, does this make me a hack discovery channel wanna be? I have actually only seen this once on tv, but I learned it on my own.

    I always felt that the weld puddle could use more heat when you are adding filler, I still control my overall heat, and do not come anywhere near fully off the pedal. It may be looked at similarly as trigger welding with a mig welder, but the modulation of heat is not completly on and off, I dont look at them as anywhere near the same.

    I also have never had any problems with cracks in welds in anything that I have built.


    The way I see it, whatever method used can acheive a very strong good weld as long as there is the correct amount of penetration, the right width of weld, and enough filler is added.

    From my perspective here are some TIG methods used by other very successful builders: Somebody please tell me if I have judged others welding wrong......


    JIMCO, Geiser, Porter = mostly "pedal pulse" welding with some weave on the Geiser, and the "pulse weave" on some sections of the Porter. All nice welding!!

    Robby's stuff= Multi Pass Weave= Bad ***** and duh....obviously strong

    SPD, Mike Smith, Dump's new Herbst machines= standard, plain, nice, strong tig weld. The quality strength and success of these vehicles speak for themselves. The Herbst new trucks will be successful in due time.
    Last edited: Aug 13, 2008
  20. garagebuilder

    garagebuilder Member

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    Brea, CA
    A lot of people in this thread have summed it up well, because most people in this thread actually fab and/or do it for a living and are not biased and stubborn because they are being mis directed by some company that fills their head with BS just to make a few extra bucks. Bottom line when it comes down to tig on thin wall space frames, get it hot, but not too hot to where you need to back purge the tube because it's trying to oxidize the back of the weld, and pound in the filler as much and as evenly as possible, to negate any chance of forming any stress risers.

    My opinion on the whole weave deal is that one day someone decided to try it out and thought it was pretty, it caught on and became trendy and an awesome way to church up some crappy fab work, kinda like fake ****.

    The argument on the third pass annealing the joint...so are you using some type of temp gauge/marking to make sure you reach a certain temperature during the weld? Thats a diaper full of BS right there, pulling off an annealing proccess by feel would be impractical, thats what a torch is for.

    Multi pass is a common pipe and structural practice, you almost never see single pass in these fields, people confuse weave with multi pass, they are different. multi pass has its place in offroad, on thick materials, and has been mentioned already in this thread. Unless your cage work is 2"x.250" multi pass has no place on tube work. What about RG chassis? The welder's background is structural pipe from my understanding, why would you not expect multi pass welds from him, a much eaisier transition doing it the way he's done it for years rather than to conform to a small industries "standards". note that I am in no way shape or form taking away from Ron's talents and abilities as i have a high level of respect for him and his work.

    Take it for what its worth, its the internet.
    Last edited: Aug 13, 2008
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