Squaring up box girder
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  1. #1
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    Default Squaring up box girder

    I am more of a welding type of guy so I don't really know what the monetary cost of machining is.


    I have a 100x100x5 girder 900mm long (offcuts I have lying around). I want it milled on each to have 4 flat surfaces square to each other.

    A girder isn't too easy to ship back and forth so if there is no one on here nearby could someone could give me an idea of what a reasonable price is? That way I can work out if local companies are giving a fair price or not.

  2. #2
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    I'll asume you really mean structural square tubing

    Impractical - unless you envision very loose tolerances for flat and square

    The 5 is too thin - it will holler on every face milling pass and though "shiney" will in no way be flat due to the milling pass releasing stresses.

    If he tries some more you will have practically no wall left

    In a word, you will be disappointed and they will find they under bid the damn thing

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    Ah thats a fair point.

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    John is right of course.
    Why don't you tell us what you need this thing for and how 'square' and 'flat' it has to be?
    I suspect there are better ways to achieve your purpose than milling.
    Just my two 'øre'!
    Regards, fusker

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    Default

    Perhaps a big surface grinder?

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    Rectangular tubing has a lot of internal stress. Removing material from one side will cause it to deform. Each time you turn it and surface another side it will move again. Chances of ever getting it straight and square are really small.

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    Quote Originally Posted by Illinoyance View Post
    Rectangular tubing has a lot of internal stress. Removing material from one side will cause it to deform. Each time you turn it and surface another side it will move again. Chances of ever getting it straight and square are really small.
    To a machinist. To a welder it may be exactly what he needs.

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    In this case it has to be machinist sort of square. The vague plan was machine the girders, fill with epoxy concrete and use then as the ways of a cnc milling machine or the bed of a cnc lathe.

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    If you insist, I guess you can make a silk purse of your sow's ears, but you should attempt to visit a successful attempt of this enterprise.

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    Quote Originally Posted by Rainbows View Post
    In this case it has to be machinist sort of square. The vague plan was machine the girders, fill with epoxy concrete and use then as the ways of a cnc milling machine or the bed of a cnc lathe.
    A way to get there is resequence and add necessaries

    "Rebar" crossing both ways (6 mm all thread) screwed thru tapped holes both walls and welded in c'sink outside

    Plugs/bungs for later tapped holes as needed - all in planned for locations - similarly welded

    THEN epoxy concrete

    THEN machined for flat and square

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    Quote Originally Posted by Rainbows View Post
    In this case it has to be machinist sort of square. The vague plan was machine the girders, fill with epoxy concrete and use then as the ways of a cnc milling machine or the bed of a cnc lathe.
    If your going to build a real C.N.C. machine, you spend real money on proper materials to build a proper machine.
    Cobbling with what you have laying around sounds like A hobby machine.

    And there is a forum for that, one that cannot
    Be listed here.

    BTW I have designed fixtures doing just what you intend, it didn't turn out good, and I redesigned
    It using different materials and techniques.
    (Eliminated machining the box tube)

    it then ended up being a economical, repeat job for my employer.

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    Quote Originally Posted by digger doug View Post
    If your going to build a real C.N.C. machine, you spend real money on proper materials to build a proper machine.
    Cobbling with what you have laying around sounds like A hobby machine.
    ...And if you are doing this as a hobby and trying to go the cheap route, then having machine work done for you is not going to fit in your definition of reasonable price.

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