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  1. #1
    Join Date
    Mar 2014
    Location
    Australia
    Posts
    4

    Question Model ARM Spindle nose Thread Damage

    Hi Folks,
    This thread is about another thread. Specifically, the thread on the spindle nose (chuck or faceplate mounting) of a friend's 9" Model ARM. It is slightly deformed.
    The 4-jaw chuck mounts satisfactorily but neither of the two 3-jaws supplied with it (used school machine) will snug up to the end of the thread. They bind about 2/3 of the way along. The thread is visibly rounded over for the first couple of pitches.
    Machine has the usual twin lever gearbox and the lead screw is true to label at 3mm pitch.

    The solution seems to be to fit a screwcutting tool to the toolpost and hand feed a threading operation to trim the sides of the thread.

    Problem is: We cannot locate information about:
    1. Details of the threadform of the spindle nose thread. Is it 3mm pitch or possibly 1/8th inch or ?
    2. What number of teeth were supplied for the stud gear and screw gears? This lathe has been used in a school and gears supplied may have been transposed.

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  3. #2
    Join Date
    Nov 2005
    Location
    adelaide
    Posts
    667

    Default

    pretty sure most hercus spindle threads on 9 inch and 260 are 8 un thread ( not unf or unc)
    john

  4. #3
    Join Date
    Jun 2007
    Location
    sydney
    Age
    64
    Posts
    3,566

    Default

    As already said the thread is 1 1/2 x 8 tpi un/uns,pitch being .125".

    The gears you should have for standard thread pitches are 20 ,45,50 and an 80 idler.

    The 20 or 50 interchange on the stud for different pitches.

    The 45 remains on the screw.

    And the 80 is the idler between the stud and screw.

    What part of Australia are you in.

  5. #4
    Join Date
    Mar 2014
    Location
    Australia
    Posts
    4

    Arrow Well - THERE'S -ya Problem.

    Thanks enormously for that information. I need to wait until the weekend to visit the machine again - but I reckon there has been a stud gear transposed - possibly from a 260!
    I'll investigate further.

    The machine is in Adelaide - It was recently put out to pasture from a school to live out its remaining years in a Garaj Mahal (decent sized mancave) about 10 clicks from where it was born. Required a really good clean, a lick of paint and a single phase downgrade from the 3 phase fitted. Still sorting out the speed control and reversing issues.

    Thanks again. - will report on the spindle thread fix in the week to come.

  6. #5
    Join Date
    Mar 2014
    Location
    Australia
    Posts
    4

    Thumbs up One small step for the Machine

    We set the ARM gear train as suggested but did not have the option of a 3.125 mm pitch due to the Metric Gearbox and leadscrew.
    Nevertheless, we used the 3.25 mm pitch (forgive me) setting with a single point tool, hand-fed the drive pulley and shaved a tiny bit from the trailing edge of the spindle nose thread for the first two pitches only.

    Success! The 3-jaw screws on and snugs up to its shoulder without effort.

    A test facing cut in aluminium was not as clean as I would like and so we looked for other sources of vibration.

    We found a minor issue with a slightly loose overhead jackshaft pulley, and the owner will attend to that soon.

    We also firmed up the gib screws on the crossslide.

    Even so, I have a sense that the spindle has lost pre-load on its roller bearings. Where can we go for information on checking /setting the bearing pre-load?

    That's the next small step...

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