milling question

Discussion in 'Motorized Bicycle General Discussion' started by junkyard, Jan 25, 2009.

  1. junkyard

    junkyard New Member

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    for the machinists out there....well jim and ret

    can you mill a square tapered hole to fit onto a 3piece bottom bracket?
     
  2. Creative Engineering

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    It's called a broach. You drill a hole first, and then use an arbor press to push a broach into the hole. The broach shaves the metal out of the corners. This is also how straight key slots are cut.

    It could also be done with a wire EDM, but it would be expensive.

    The milling machine will always leave a radius in the corners.

    Jim
     
  3. Retmachinist

    Retmachinist New Member

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    I'm not sure what you mean "to fit into a 3 piece bottom bracket?" Milling wouldn't be an option. There are ways to cut square holes, broaches, E.D.M.'s, lazers, water jet, also not sure why you need a tapered square hole? Explain.

    John
     
  4. Creative Engineering

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    I think he's talking about the pedal crank shaft.

    I've got the 3 piece set-up on my Spoilers. The shaft is square and tapered at the ends 2-3 degrees.

    The hole in the crank has a corresponding square, tapered hole so that the crank is forced onto the taper for a positive fit. There is a bolt that draws the crank onto the shaft.

    Jim
     
  5. junkyard

    junkyard New Member

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    you said the magic word....expensive

    ok even tho i love the clean look of the bottom bracket jackshaft im probly gunna try to use a steel hub like i did on my electric drive conversion

    thx for the info
     
  6. junkyard

    junkyard New Member

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    yes what jim said....to fit onto the bottom bracket like the crank would....sorry for any confusion

    edit:the idea was to make a piece for one side to mount 2 freewheels back to back and a piece for the other to mount the larger sprocket to the engine......both pieces would bolt onto a standard bottom bracket

    but the idea revolved around making the square tapering hole like a crank arm has
     
    #6 junkyard, Jan 25, 2009
    Last edited: Jan 25, 2009
  7. Retmachinist

    Retmachinist New Member

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    O.K. I am with you guys now. I thought at first he wanted to cut a tapered square hole through the bottom bracket, just tapered at one end. I couldn't figure out what you could use it for.
    Got it now.

    John
     

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