Welding newbie need advice

Discussion in 'Motorized Bicycle Welding, Fabrication and Paintin' started by ferball, Mar 30, 2011.

  1. ferball

    ferball New Member

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    I am new to welding, took some classes years ago and have forgotten most of it. I have a cheap HF Mig welder. It works great, but the welds are not pretty. My big question is this: The bike frames I have vary in material. one of the frames is an old french thing with nice heavy steel frame, I weld a walmart special with the thinner oversized tube to it and get crappy looking welds of questionable integrity. The problem is that the different gauge metals, if I set it hot enough for decent penetration of the french frame, it just melts the walmart tube, if I turn it down to for the walmart tube, then I don't get penetration on the french frame. any suggestions? I have been laying on the welds and grinding down, an it is ugly, but it seems to hold, but I figure someone might be able to give me some pointers for better welds and less grinding.
     
  2. Venice Motor Bikes

    Venice Motor Bikes Custom Builder / Dealer/Los Angeles

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    Sometimes you can just 'trigger' it... It's kinda like doing spot welds one at a time in a chain, letting each one cool for a few seconds before starting the next. The finished weld looks proper, 'like a stack of coins'.

    Practice doing it for a while before trying it on a good frame.
     
  3. 2door

    2door Moderator
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    Venice gives good advice. Trying to get good penetration when welding thin metals sometimes requires a stop-and-weld method. This means doing a short bead, stopping and then welding again. Practice on some scrap metal. Find some about the same thicknes of the project you're working on and give the weld-stop-weld method a try.
    Running long or continous beads on thin material is hard and requires a lot of practice. The stop-and-go method will help.
    Also on a MIG machine, the slower your wire feed speed, the hotter the weld. I don't know if your machine has an adjustable wire feed speed but try speeding it up for thinnner material.
    Tom
     
  4. DaveC

    DaveC Member

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    It's like the trick I've used when welding mild steel to chrome-moly, spend more time on the thicker part. We're not talking all that much more time, just enough to even the heat out.
     
  5. motorbiker

    motorbiker New Member

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    A mig is constant voltage. The wire speed is the current.

    In MIG welding amps are adjusted by changing wire speed. The higher the wire speed the more amps.

    For thinner metal you would want to slow the wire speed down and adjust the voltage.

    If the voltage is too low the wire will hit the puddle. If the voltage is too high the arc will be too big and there will be lots of spatter.
     
    #5 motorbiker, Mar 31, 2011
    Last edited: Mar 31, 2011
  6. "the prussian" Shop Dogs

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    You can also try sleveing the thiner tube with a chunk of pipe , are these dismillar metals ? If you have a grinder see what the grind spark looks like . High carbon (black) steel pipe is never going to bond to cromeoly steel very well . You may have better luck brazing then mig.
    Spotting works to keep temp down ,but creates areas of slag inclusion that weakens joint strength. Like anything else everybody has there opnion and tech. That work for what they want to do . Good luck.
     
  7. motorbiker

    motorbiker New Member

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    Copper makes a good backing plate. Helps with thin metal. The weld won't stick to the copper.

    That is what I used to weld a thick 1" piece of pipe to a thin 55 gallon drum.
     
    #7 motorbiker, Mar 31, 2011
    Last edited: Mar 31, 2011
  8. ferball

    ferball New Member

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    Thanks for all the tips, is there any way to check joint/weld integrity without fancy equipment aside from whacking it with a hammer and putting some weight on it? I think the welds I have will hold, and they have withstood the hammer and I can put weight on it, but with long term use will welds give way, or is it the metal they are bonded to that give up?
     
  9. motorbiker

    motorbiker New Member

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    X ray ?

    I would try on some scrap bike stuff and bend them and see how strong your welds are.

    I look at bikes at WalMart every time I go while the wife shops.

    Seen some pretty bad looking welds.
     
  10. "the prussian" Shop Dogs

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    For most home shops, your best indicator of joint intergity is viewing the "puddle" during running the bead. If you see good penatration and the bead has a nice fillet to the edge, it's probly fine . You can test with hammer ,but better maybe to cut across a test bead and view cross section of test weld . Remember the better the mech. Fit to start, with good surface prep, the better the weld no matter what pross. You use.
    Backing with brass or copper is a good tech to learn with mig , works well with thin sheet app. Just remember it can still melt or burn thru.
    With mig and diffrent metal dim. A tech. Called "horseshoe bead" may be of use . One starts the puddle on the thicker matt. Then runs up onto thiner matt. And back off again making little swirls or "horseshoes" . This generaly only works with mig ,but is similar to a brazing torch pattern .
    Clean and grind well and you'll weld well ,chamfer ends and use root and covering passes if ness. Most of all pratice alot!
    Some good projects ,like arm rests, will let you pratice and make shop eqip. At the same time.
    I just started teaching my friends kid to weld , he made an engine stand out of an old kids bike , i don't know how i ever got along without it.
     
  11. 2door

    2door Moderator
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    All MIG machines are not the same. I have settings for volts, amps and wire feed speed.
    For deeper penetration on thick material you'll want to slow the feed and increase output voltage. That way the arc stays concentrated longer in a given area, hence deeper penetration. On thin stuff you'll want to move fast to decrease the chance of burn through.
    The copper backing idea is a good one for thin materials. The copper absorbs some of the heat and makes longer beads without stopping possible. I've used copper to back up behind a hole I needed to fill in sheetmetal. The steel filler won't stick to the copper and when the hole is filled just pull it off.
    Tom
     
  12. motorbiker

    motorbiker New Member

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    For deeper penetration using mig you would want more amps, more wire speed.

    I went to school for welding and welded for years making a living.

    I am sure more wire speed = more amps.

    I also am an electronic tech.

    Thick metal, turn up the wire speed, more amps and adjust the voltage so that the wire does not hit the puddle.

    Thin metal, turn down the wire speed, less amps and adjust the voltage so the wire does not hit the puddle.

    If you slow the wire speed and increase the voltage too much the arc will be too large and little pieces of metal will fly all over.

    This is called spatter. Those little balls of metal around welds. This does not increase penetration.

    Mig 101
     
    #12 motorbiker, Mar 31, 2011
    Last edited: Mar 31, 2011
  13. motorbiker

    motorbiker New Member

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    In stick welding, wire speed would be feed speed or how fast that rod burns.

    Turn up the amps on a stick welder and the rod will burn faster and you will have to feed it faster.

    Stick welding is constant current.

    In stick welding the voltage changes when you lift the rod away from the puddle or closer to the puddle. The current stays the same.

    Like in mig if the voltage is too high the rod or wire will be too far away from the puddle and lots of spatter and little penetration.

    Either way if you want to use a faster wire speed or burn rod faster you need more current = more heat.

    With thinner metals you need to use less heat to prevent burn through.

    Smaller wire or rods, less amps, slower wire speed.

    http://www.hobartwelders.com/weldtalk/showthread.php?p=51927#post51927
     
    #13 motorbiker, Mar 31, 2011
    Last edited: Mar 31, 2011
  14. Crazy Horse

    Crazy Horse Dealer

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  15. motorbiker

    motorbiker New Member

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  16. 2door

    2door Moderator
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    Check post #6. The man says in essence, "whatever works for you". I've never made my living as a welder but I too went to school for it and have been welding since the mid 60s. I have MIG, TIG and arc machines in my garage.I have Oxy-Act too but use it only for brazing and heating.
    Welding, like any other trade has people from both sides of the bridge. My advice was based on many many successful welds building cars, airplanes and other projects. I've never had a weld fail.
    Let's not get into an augument over a process that has opposing followers. You learned one way; I learned another. If we both have success...so be it. Okay?
    Tom
     
  17. turtle tedd

    turtle tedd Member

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    2-DOOR says "All MIG machines are not the same"...Believe this before anything else and go from there.....may I say , as I have said many times before.. gas must be used with any type of MIG welding no matter what type of wire is used or what type of material is being welded
     
  18. ferball

    ferball New Member

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    I appreciate all the input, I increased the wire speed as suggested. My welds look tons better and I feel much better about them. I also used the "horseshoe" technique that was suggested for disimiliar metal thickness, that worked well. Thanks for all the advice and info. This is why i love this forum.
     
  19. "the prussian" Shop Dogs

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    Glad to hear you had some success. Learning to weld is a life long process that can be as rewarding as it can be aggravating. I spent ten years as a shipwright for the u.s. Navy , we used every welding process you can imagine and some even i still don't belive. Under water and under way . Just ease into it and pratice alot . Like any other skill it comes with time. Theres nothing like rolling(or floating) out on something you made yourself.
     
  20. flybytaco

    flybytaco Metal Molding Madman

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    ya i was gonna tell you start on the thick frame and work into the thinner stuff always.
     

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