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Thread: What has happened here?

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    Default What has happened here?

    I'm a bit embarrassed to post this as I absolutely cooked this joint but something has gone drastically wrong and I want to learn from this.

    I was brazing in this dropout when I realised things were not going well and so I decided to pull the pin. I began to heat up the whole joint so I could pull the dropout out of the slot when suddenly it came loose and the fork blade split in this unusual way. I don't understand how a non hardened steel could crack like this. It appears to have come from the ends of the slot so I'm assuming it's something I've done. I slotted the blade on the mill with a slitting saw and I'm thinking maybe I went to fast here and that has caused a fracture or something? Thoughts?

    Also another question, the blade is Columbus Max, and I had the shop I ordered from bend the blades for me as I don't have a bender. They have heated the blades up to bend them, is this normal/ok? I've never seen anyone use heat to bend a fork blade.

    Thanks
    Scott CundyIMG_0636 copy.jpgIMG_0639 copy.jpg

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    Default Re: What has happened here?

    Heat in the wrong place and metal tore away as you tried to remove the dropout. Nothing wrong with the tube, remember we are talking about a wall thickness of about one mm so we need to be a bit delicate when manipulating.
    Bill Fernance
    Bicycle Shop Owner
    Part Time Framebuilder
    Bicycle Tragic

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    Default Re: What has happened here?

    Looks like liquid metal embrittlement to me.

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    Default Re: What has happened here?

    For a tabbed and slotted dropout…

    If you’re doing a repair, replacement, or simply undoing a brazing task, always have the forged part in the air with the blade held at vertical. Only heat the dropout (only - remember this) until the filler material is in a liquid state. Then commit to pulling the part straight up without wiggling right, left, or sideways. Your blade broke because it was too hot, maybe under load owing to a tight slot, and your bending pattern during the pull.

    It’s simple but not always easy.

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    Default Re: What has happened here?

    @brewery: your post implies that the damage occured before you began to pull the dropout. Can you confirm this?

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    Default Re: What has happened here?

    Using heat to bend the blade isn't odd or taboo, and didn't contribute to this situation.

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    Default Re: What has happened here?

    Quote Originally Posted by Mark Kelly View Post
    @brewery: your post implies that the damage occured before you began to pull the dropout. Can you confirm this?
    There was no sign of any damage to the blade before I started brazing and certainly no sign of the cracks (that I noticed) before I started to pull the dropout. I was just hypothesising as to what could possibly have caused this and thought that maybe some sort of hairline crack had formed when I slotted the blade but it sounds like it was just me making amateur mistakes while brazing.

    When I pulled the dropout I was just generally heating the whole area, not just the dropout, so it sounds like I got everything a bit hot and stuffed up.

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    Default Re: What has happened here?

    Quote Originally Posted by brewery View Post
    There was no sign of any damage to the blade before I started brazing and certainly no sign of the cracks (that I noticed) before I started to pull the dropout. I was just hypothesising as to what could possibly have caused this and thought that maybe some sort of hairline crack had formed when I slotted the blade but it sounds like it was just me making amateur mistakes while brazing.

    When I pulled the dropout I was just generally heating the whole area, not just the dropout, so it sounds like I got everything a bit hot and stuffed up.

    Never (ever) heat the blade. Heat the forged or cast part and it will bring the blade up to temp.

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