Casting BB Shells

benneally
benneally Posts: 973
edited May 2012 in Workshop
Does anyone know, or know where to find, information on casting bottom bracket shells? I am just keen to understand how they make the casting hollow and make the entry holes for the down tube/seat tube/chain stays?

Thanks
Scott Spark 30 Boardman Road Comp Fixie Mud Aero Rims

Comments

  • Rule74Please
    Rule74Please Posts: 307
    In what material?

    I can explain for you Shame is they are not cast
    Don't know the Rules?

    http://www.velominati.com/blog/the-rules/
  • benneally
    benneally Posts: 973
    Either steel or titanium.

    What's shame?
    Scott Spark 30 Boardman Road Comp Fixie Mud Aero Rims
  • proto
    proto Posts: 1,483
    Google 'Investment Casting' or 'Lost Wax Casting' and all will be revealed.
  • benneally
    benneally Posts: 973
    I've already done extensive googling, but cannot find images or a method to support my hypothesis of how the mould fits together.
    Scott Spark 30 Boardman Road Comp Fixie Mud Aero Rims
  • nicklouse
    nicklouse Posts: 50,673
    benneally wrote:
    I've already done extensive googling, but cannot find images or a method to support my hypothesis of how the mould fits together.
    What makes you think they are cast?
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • steelie600
    steelie600 Posts: 519
    nicklouse wrote:
    What makes you think they are cast?

    Very good point, My bb is CNC machined from billet, then the tubes are welded on to that.

    I wouldnt have thought that there are many, if at all any cast bb's nowadays. But as some one pointed out, wax moulding is how id do it.
    Idiot ^^^^^^^^^

    Ralph
  • proto
    proto Posts: 1,483
    Check out this video on YouTube:

    http://www.youtube.com/watch?v=BX8w-GUP ... ata_player


    Sent from my iPad
  • benneally
    benneally Posts: 973
    These are all titanium cast, and you can see the bottom bracket shell at the top.

    http://www.allotec.com.tw/Product-200710813561-l.jpg
    Scott Spark 30 Boardman Road Comp Fixie Mud Aero Rims
  • sungod
    sungod Posts: 17,504
    benneally wrote:
    I've already done extensive googling, but cannot find images or a method to support my hypothesis of how the mould fits together.

    for investment casting, the mould doesn't "fit together"

    a wax pattern of the desired shape is produced, one or more runners are attached, it's dipped in ceramic glop, the glop hardens (several dip/harden cycles may be used), then fired to melt/burn off the wax

    the mould is heated, the molten casting metal is poured into the mould, which may be in a vacuum or non-reactive atmosphere, it cools, you smash the mould off

    parts are snapped/cut from the runners, and finished, some may need to undergo subsequent heat or surface treatment
    my bike - faster than god's and twice as shiny
  • benneally
    benneally Posts: 973
    Thanks sungod. Yes that is the basic method for casting solid objects.

    But if you are casting hollow items, you have cores that are inserted into the moulds and then removed. I am interested in how the cores for the bb shells are removed, and i assume to make the interconnecting hollow passages, that you have a mould of the internal shape of the bb shell, that is then dunked in the wax, and then that is dunked in ceramic slurry, blah blah.

    Im just looking for info on the core..? Any ideas?
    Scott Spark 30 Boardman Road Comp Fixie Mud Aero Rims
  • MichaelW
    MichaelW Posts: 2,164
    There was an old article on making lugs by investment casting and stamping.
    reproduced here.
  • sungod
    sungod Posts: 17,504
    benneally wrote:
    Thanks sungod. Yes that is the basic method for casting solid objects.

    But if you are casting hollow items, you have cores that are inserted into the moulds and then removed. I am interested in how the cores for the bb shells are removed, and i assume to make the interconnecting hollow passages, that you have a mould of the internal shape of the bb shell, that is then dunked in the wax, and then that is dunked in ceramic slurry, blah blah.

    Im just looking for info on the core..? Any ideas?

    for many items, the wax pattern is easy to create in the shape of the final item, you dip it, the entire surface is coated, inside and out, there's no core to be inserted

    to create the wax pattern may require a skilled person to assemble it from several pieces, using a heated tool to 'weld' the bits together

    once the ceramic has hardened and you bake out the wax, you have a ceramic shell with a void in it the shape of the final item - there are no cores required

    you then fill this void with metal - to avoid air pockets, you must either do it in a vacuum or add runners to allow the air/gas to escape and metal to flow through the entire void

    for a bb shell i think you can do it as above, it's a simple shape

    but, finally answering your question about cores i hope, if the shape is complex then the wax pattern may itself have ceramic parts embedded in it, with exposed supports that will eventually be held by the outer dipped ceramic

    there's a nice example of this here, see the third page...

    http://www.platinummetalsreview.com/pdf ... 17-126.pdf
    my bike - faster than god's and twice as shiny

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