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Is there such a thing as cast Chrome-Molly?

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  • Is there such a thing as cast Chrome-Molly?

    I'm working on a BMX bike. I'm building it out of my wife's old Mt bike. It is a Nishiki Colorado. It has a CRMO frame.

    Here is my problem, the Mt bike frame has axle cutouts that face down, and the chain is adjusted by the derailler. ON a BMX bike, the cutouts are horizontal and you adjust the chain by moving the axle forward or back. I haven't put a chain on it yet, but if it ain't just right, then it will throw the chain. I was going to make a chain tensioner, but I just got the idea of changing the wheel mounting plates to horizontal.

    The bike has a CRMO frame, but the axle mounts are cast. The are slipped into the end of the tubing and then brazed. Would they be cast CRMO or steel? The only thing that I have to weld with is a HH 125 or a torch. I'd probably use a torch as I think that it would give a better looking weld.

  • #2
    Hey Stinky,
    Yes, there are chrome-moly castings. You didn't indicate the wall thickness of the frame tubing or the thickness of the wheel mounting plates. You need to provide all relevent data for the members to suggest a solid modification.

    Since the original setup was brazed, you could could do the same or silver-solder. You have to consider the HAZ when heating the joint with O/A for brazing. I don't really see any negative effects using MIG if the thickness of the plate are within the heat range of your welder. If your 125 doesn't have enough power, find someone with a larger MIG to help you.

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    • #3
      The frame tubes are made from double-butted CRMO. They put them in a mandrill and push the metal from the center of the tubing out to the ends (Or so I've been told). Anyway, on the tubing, the ends are thicker than the middles and I would expect the ends to be in the 1/16" range.

      The flanges, they are about 3/16" thick. I said cast, but they may be forged.

      I assume the CRMO is ferro-magnetic? In fact, now that I think about it, that is what I'd expect on the bike, now that I think about it. But, they could make it a smidgen thicker and it would be a whole lot cheaper to make and just a bit heavier. But, on my kids bikes, the flanges are thinner, so this is already thicker and should have plenty of excess strength to it.


      • #4
        Originally posted by Stinky View Post
        The flanges, they are about 3/16" thick. I said cast, but they may be forged.

        Highly unlikely that a thin fork-shaped or slotted item would be "cast".
        If it has that surface appearence, it may be forged or more likely
        stamped with dies textured to give an embossed appearence.
        Last edited by vicegrip; 09-05-2010, 09:19 AM.
        Negative people have a problem for every solution


        • #5
          Perhaps forged dropouts?

          However, some are investment cast:
          --- RJL ----------------------------------------------

          Ordinarily I'm insane, but I have lucid moments when I'm merely stupid.


          • #6
            Originally posted by usmcpop View Post

            However, some are investment cast:
            That would be a lot less stock-scrap that stamping
            and easier to controll the process than forging.
            Bet yer right. D!ck
            Negative people have a problem for every solution