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  • AC Arc welding cast iron?

    I have a little job to do, sawing the bottom off a 3-point steady (wrong height for my lathe, otherwise Just Right, and Free) and (I hope) welding it back on, want a bit of advice...

    I have an AC Arc welder (an old Oxford oil-cooled, 110Amp), from what I've read I should use either nickel or cast-iron rods, but everything I've seen says DC, can I get away with AC?

    If I wanted to weld the cast-iron steady frame to mild steel, would it be possible, assume I'd need to use nickel rods for this, preheat the work and peen the hot weld as I would for cast iron?

    Thanks peeps,
    Dave H.
    Rules are for the obedience of fools, and the guidance of wise men.

    Holbrook Model C Number 13 lathe, Testa 2U universal mill, bikes and tools

  • #2
    You don't say what kind of lathe this is but if it is Chinese that thing may not even be weldable. You should try welding on a small section (maybe a corner?) before sawing this thing to see if it will weld ok. It's common for someone to ask about welding "cast iron" without saying what kind of cast iron, but then they rarely have a way of knowing. The fact is there are many types of iron castings and some weld just fine while others can be extremely difficult, then there are some castings that can be near impossible to weld. In any case you would most likely have much better luck doing this with Oxy/Acetylene and bronze brazing rod, the brazing process will successfully weld a wider range of casting types and in most cases make a stronger joint on a part such as this. If you do decide to arc weld it then use a Nickel rod such as Ni55 but don't even consider using ANY kind of carbon steel filler such as 7018 or MIG wire.

    BTW, the really expen$ive Ni 99 rods are, contrary to popular thought, not stronger or necessarily a better choice. The only advantage they offer is that they produce a machinable weld but unless you need to machine finish the welded area using them is not necessary nor advised.
    Last edited by radkins; 11-05-2011, 10:15 AM.

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    • #3
      Steady Rest Modification

      This shows an alternative to welding.


      After sawing the old base off a new steel plate was made to fit the ways. Two holes were tapped at the appropriate locations and bolts were installed. The plate was attached by casting the cavity full of Devcon liquid steel.
      Byron Boucher
      Burnet, TX

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      • #4
        Hmm, some food for thought...

        The lathe's definitely not Chinese, quite the opposite (2 tons of 1950's Holbrook toolroom lathe), but the steady is - raided from the scrap bin

        Radkins, as I don't have O/A welding gear, but have a carbon-arc tap on the arc welder, could I arc-braze? I have some carbon rods, silicon bronze filler wire and a jar of brazing flux... I imagine I'd get much less distortion, perhaps little enough that I could pretty much finish the new base before brazing?

        Boucher, bolted construction was something I considered, but I wasn't convinced it'd be rigid enough - how has yours been in use?

        I have some cast iron (I hope suitable) to make the new base (end frame of a Chinese bending brake that fell off a truck and cracked a mounting lug off, scrap bin again), it should be thick enough (1" plus) to cut the vee for the ways and have enough meat to drill a counterbored hole each side to screw to the steady frame - M8 x 30mm capscrews maybe? I wonder if it's worth bolting then brazing?

        Thanks for the help, gents
        Dave H.
        Rules are for the obedience of fools, and the guidance of wise men.

        Holbrook Model C Number 13 lathe, Testa 2U universal mill, bikes and tools

        Comment


        • #5
          Originally posted by Hopefuldave
          Radkins, as I don't have O/A welding gear, but have a carbon-arc tap on the arc welder, could I arc-braze? I have some carbon rods, silicon bronze filler wire and a jar of brazing flux... I imagine I'd get much less distortion, perhaps little enough that I could pretty much finish the new base before brazing?.

          While one of those things can used to braze with, and would likely do a decent job of "tinning" the surfaces of the parts it might be difficult for a deep and/or closely fitting joint. I strongly recommend tinning both surfaces rather than try to get the filler to flow onto the bare iron surfaces in a deep or closely fitted joint, if that material is what I suspect it is then tinning first may be the only way to get a decent union.

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          • #6
            Dave, I used a 3” X 1/2" plate for my base. The holes in the base were threaded for 1/2" bolts, which became pillars that were cast into the Devcon liquid steel epoxy. The inside of the steady was cleaned with Acetone.
            There is a lot of bond area and this is a very rigid assembly. It has worked very well for over ten years.
            Byron Boucher
            Burnet, TX

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