mig welding tip distance

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i have a small cheapo mig welder i am using to learn and i am wondering what is the "correct" tip to work distance? also i read that you should not be getting splatter on a good mig weld, and my welds always have splatter. also, i am working on building a trailer, and i am hoping my welds are strong enough. to test them i got a sledgehammer and tried to knock one of the welds apart, and it took three or four good whacks to knock a peice of 2"x3" angle off that i butt welded to another peice. also i can stand and jump up and down on any part of it without it breaking.  does that sound reasonable? one last question, if i do a weld that i don't think got good penetration, i go back and put a new bead on either side of the old one. is this a good idea or does it just heat it too much and weaken it? thanks alot
Reply:Without looking it up (been a long time) I'm gonna say around 3/8ths of an inch from the tip to the work piece. I tend to run too close once in a while. I like sizzle instead of crackle ... Once you get the hang of visibility you can do everywhere from long to short depending on what you need for puddle control.As far as the "destruction testing" you did, I'd be leary of anything I could knock off at all without nearly destroying one or both pieces. If you were making a decorative trellis, that's one thing, but a trailer is more serious than that. Not only can it be dangerous but it'll fail you at the worst possible time. Keep practicing till you get tired of beating on it before it gives in. The second or third pass thing is sort of a tough call. That's more of a situational thing. You could be only adding to the warpage without doing anything on a scale to increase strength. Not much sense in having 3/8ths worth of bead on 1/8th material. But if you need an additional pass to get up to the fillet requirements then yeh, do it.
Reply:OOPs,I just read a little closer. You said if you "didn't" think you had good penetration. Sorry. In those cases I usually bite the bullet and gouge it out. Good for the learning curve. Poor penetration or no penetration is a built in crack starter. Successive layers might slow it down but the starter kit is there. If there was insufficient heat to get good penetration to begin with additional layers isn't going to do much for you unless you've made some serious adjustments before proceeding. Run high and hot.  It's your welder. You own the knobs .. Crank that puppy up.
Reply:I, too, have a small mig, but if I were considering building a trailer, I would grab my good ol' Lincoln stick welder to be sure I had maximum penetration on the welds, and save the mig for small stuff.  What thickness of metal do you plan to use to fab the trailer?
Reply:The "stickout" can be anywhere from 1/4" to 3/4". As Sandy suggested, I find most often that my stickout is about 3/8" to 1/2". The best way to see if you're getting enough penetration is to weld one side of a "T" joint & break it in a vise with a sledge hammer. GMAW actually has a higher current density which concentrates more current at one point than with SMAW, producing greater penetration. The relationship between current & penetration is direct. If you are not getting satisfactory penetration, first, try increasing your wire speed until it begins stubbing, then back it off slowly until stubbing stops. If you are still experiencing a lack of penetration, try decreasing your stickout distance. If you are still not satisfied, other considerations(in this order) are; a) use a pulling, rather than pushing technique.b) reduce wire size.I am assuming that you're using CO2 for shielding, not C25 or another blend/gas. Chances are, the spatter that you're experiencing will be reduced by the above suggestions. GMAW is not a spatter-free process, though you should have less spatter than with SMAW. Still, don't be concerned if there is a lot of spatter on your nozzle, that's just the way it works! You may be using a machine which is not capable of satisfactorily welding the thickness of the plate that you are using. I don't remember if you mentioned the type/capacity of your machine...Hope this helpsMike
Reply:Almost forgot... like Sandy said, if you are not sure if you have sufficient penetration, don't multi-pass it, as the joint will tear from the root & your result could be a starring role on the 6 o'clock news! Cut it out & start again!
Reply:"small cheapo mig welders" are not for welding trailers.Not what you wanted to hear, but what you need to know.You WILL get spatter from GMAW, ESPECIALLY from underpowered units that are cranked way up in an attempt to make them do things they should not be doing.Beads laying on the top of a weldment are sure recipes for failure.  And the most common ingredient is a "small cheapo mig welder" (your words.)Don't think I'm being a jerk.  You just don't have the equipment to do the job anymore than if you had a hot glue gun.What's the thickness of that 2x3 angle?  1/4"?Now, to answer your question and give you the best performance out of what you have for doing things other than trailers and bridges, I like to hold about a 3/8 - 1/2" stickout on small MIGs.  Spatter increases with amperage to a degree, though it is still usually very little, especially with an argon mix.  CO2 has more penetration as well as a little more spatter, but still nothing like the smoke, slag, and heavy spatter of SMAW.BTW, when you need that machine's maximum penetration, you need to with the FCAW process.  That is, anything over 1/8" as a general rule.  FCAW can bring your capability up to 3/16" and that's still only for critical components in the hands of the very experienced.Now feel free to hate me, sorry...
Reply:MAC - my Dad was a machinist/welder for PSEG for years and he says the same thing about my MM 175. I know for a fact he's never used a modern mig machine - his current shop uses only Miller Tig machines on aluminum. I'd be curious of your opinion of the MM 175 and it's ability to do larger material, like the 1/4" trailer work described above. I guess its too late for me since I bought it, but I was hoping it was up to the challange.MM 175 w/ spoolgun
Reply:Originally Posted by MAC702"small cheapo mig welders" are not for welding trailers.Not what you wanted to hear, but what you need to know.Now feel free to hate me, sorry...
Reply:oh by the way it's FCAW not GMAW doesn't that affect the spatter? and the steel i was goign to use is 2"x3"x3/16"
Reply:Originally Posted by mjohnson1oh by the way it's FCAW not GMAW doesn't that affect the spatter? and the steel i was goign to use is 2"x3"x3/16"
Reply:Originally Posted by mribeiroMAC - my Dad was a machinist/welder for PSEG for years and he says the same thing about my MM 175. I know for a fact he's never used a modern mig machine - his current shop uses only Miller Tig machines on aluminum. I'd be curious of your opinion of the MM 175 and it's ability to do larger material, like the 1/4" trailer work described above. I guess its too late for me since I bought it, but I was hoping it was up to the challange.
Reply:In GMAW, with a constant voltage power supply, as the tip-to-work distance is increased, current decreases.  So, closer = more current = more penetration.
Reply:Mac - Thanks for the advise. The dealer says that Miller forgot to send me something with the SGA & gun. From the directions it looks like I have everything I need, but in case there are any supplamental parts or instructions, I'm afraid to use it yet - so, my long winded answer could have been "I don't know yet" mjohnson - didn't mean to hijack your post - I'm sorry.MM 175 w/ spoolgun