spot welding questions

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Hey all. I have a spot welding question. My weld beads are very strong and I clean my metal very well and all that stuff. I have done a ton of research and reading about welding techniques and theory and I know I am not that great and by no means an expert, but I think I have decent skills for someone whos self taught.Now for my question. My spot welds seem to be lacking something, no matter the thickness of metal and my welders settings. They are never very strong. I am not sure if they should be stronger or I am doing something wrong in the process. For an example. I was welding a brew stand for my buddy that was 2x2 11 guage steel tubing. I was welding a section that was about two feet long so I tacked all four corners and was using a wire wheel on an angle grinder. I pushed a little hard on the wheel at the end of the 2 foot section (lot of leverage) and the wire wheel bit on that piece and broke all four of my tacks. Is that normal? That seemed a little weak to me. Now for my machine. Dont laugh please.Its a northern tool 135 amp 120 volt MIG. I bought it initially to see if welding was something I liked as much as I thought I would. Plus I bought it to do a job on my exhaust that would have cost twice the price of the welder had I farmed it out. I am more than happy with this machine for what it is, but sometime in the future would like to upgrade to a 220v Miller as I realize the limitations of a 120 volt MIG. TIG welder first though. I am using .030 wire with 25/75 gas. And like I stated previously, any setting and any metal thickness, I am not impressed with my tack welds. I dont know if the machine is not powerful enought to build up enough heat in the time it takes to make a tack? Not sure. Any advice would be much appreciated.
Reply:First off, spot weld and tack weld are different things.  You are referring to tack welds.A picture says a thousand words and can explain alot of what is going on.  Make sure it's a crisp close up picture showing weld.Nothing is wrong with a 110v mig machine as alot of people start that way, just understand they have limitations.  And for the love of god, do not ever post about wanting to build a trailer here or you will suffer a most painful flaming.    As far as 11 ga, your machine is plenty capable.I usually hold my tacks for a full second or two and swirl or make sure arc aims at both pieces.   Grind your mil scale off so you have shiny metal, mil scale takes more heat than shiny steel and when you do quick tacks it doesn't penetrate into the steel.  What heat setting are you using?  For 11 ga you should be in the upper range for good penetration.  Did you start with flux core and swith up solid wire with gas?  If so, did you change your polarity?   Try grounding directly to you piece.  I've got to go work now but if you post a picture it will help.Sent from my SCH-I545 using Tapatalk
Reply:Hey, thanks for the reply! Ive always called tacks spot welds ha, thats pretty funny because it didnt click that they are different until you pointed it out!As for the flaming thats why I said dont laugh please haha. I know my machine and I are at the bottom of the barrel compared to most people and their equipment on this site. Theres a ton of talent here and even though I think I am a DECENT welder I would be borderline embarrassed to show pics of my beads here.I dont have any pics right now but I will probably be able to get some this weekend. I always prep until all the millscale is gone and its shiny bare metal. For the stand, I welded it the entire time with my machine maxed out at number 4, the 135 amp setting. Ive only welded with flux core once and thats cause I ran out of gas, but my polarity is correct for solid wire and shielding gas currently. As far as grounding I always try to get my clamp as close to my work as possible.
Reply:Heres some pics of my beads on the stand I talked about earlier. Ive always wondered about my tack welds because Ive noticed that the heat affected zone is much smaller at the beginning of my welds. I dont know if thats every machine or if mine just starts out super cold hence the bad tacks?Last edited by Threadkiller; 04-25-2014 at 07:21 AM.
Reply:Welds made on the edge of the square tube look fine. They are flat and seem to be wetting nicely into both pieces of metal. On the other hand, the filet weld between the two pieces of tubing at 90º seems fairly crowned and doesn't seem to we well on the metal. This usually is telling you that the weld is cold. You need to make a hotter weld, which can be acomplished setting your machine hotter, lowering the wire feed speed or both at the same time.Other than that, you shouldn't be embarrrased to show those pictures here. They look pretty decent.Regarding your observation about the heat zone being bigger at the end of the weld... well... it is spot on. The heat accumulates as you keep on welding.And you guessed it, tack welds with MIG are usually cold. You need to set the machine higher than you would usually set it for that material thickness and hold longer. Not just half a second, but a nice full second (sometimes two).Mikel
Reply:Well thank you I appreciate the compliment and the advice. I did notice that the fillet welds seemed much colder looking. I wonder why? My machine was on max setting, should I just lower the wire speed and just try to tack as long as I can without building it up too much?
Reply:Are your fillet welds done in horizontal or vertical position?   I agree with mikel.  Try manipulating your torch a bit more to aim the arc onto each side and let it linger long enough on each side to wet in.Sent from my SCH-I545 using Tapatalk