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Thread: Deep thoughts...metric threading

  1. #11
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    Quote Originally Posted by Paul Alciatore View Post
    Ain't math grand.

    Your next revaluation will be that a quick change gear box that was designed for English threads is not ideal for metric ones. Different kinds of sequences. You will need several different manually changed gears to cover the range of metrics.
    Is that really true?

    If you have the maths to effectively convert your imperial screw to 6mm pitch you can cut:-


    TPI metric pitch
    192 0.25
    160 0.30
    96 0.50
    80 0.60
    64 0.75
    48 1.0
    32 1.50
    16 3.0
    8 6.0


    https://www.youtube.com/watch?v=PbpYqUccOd4



    John
    Last edited by The Artful Bodger; 04-06-2019 at 07:12 PM.

  2. #12
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    Quote Originally Posted by Paul Alciatore View Post
    Ain't math grand.

    Your next revaluation will be that a quick change gear box that was designed for English threads is not ideal for metric ones. Different kinds of sequences. You will need several different manually changed gears to cover the range of metrics.
    Unless it's done correctly - my Holbrook drives the cone of gears in the QCGB for Imperial threads, takes leadscrew drive from the plain gear; for metric threads it drives plain gear (swap of gears onto other shaft required) and takes the leadscrew drive from the cone by flipping a lever - simple and effective

    Leaves the threading dial as an obstacle, but the maker's manual's recommendation is cut and reverse without disengaging the half-nuts, whether Imperial or Metric threads are being cut, as it has a hefty brake and 3-phase plug-reverse on the motor.

    Dave H. (the other one)
    Rules are for the obedience of fools, and the guidance of wise men.

    Holbrook Model C Number 13 lathe, Testa 2U universal mill, bikes and tools

  3. #13
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    Don't know why you'd bother doing a mechanical conversion on such a late. Electronic leadscrew all the way.

  4. #14
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    Quote Originally Posted by Sun God View Post
    Don't know why you'd bother doing a mechanical conversion on such a late. Electronic leadscrew all the way.
    Why go partway? Just go CNC and never look back.......
    1601

    Keep eye on ball.
    Hashim Khan

  5. #15
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    Here is a spreadsheet I made a few years ago for various thread pitches using the HF 9x20 lathe or equivalent:

    http://enginuitysystems.com/pix/tool...hreadChart.xls

    Something like this:


  6. #16
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    Quote Originally Posted by The Artful Bodger View Post
    Is that really true?

    If you have the maths to effectively convert your imperial screw to 6mm pitch you can cut:-


    TPI metric pitch
    192 0.25
    160 0.30
    96 0.50
    80 0.60
    64 0.75
    48 1.0
    32 1.50
    16 3.0
    8 6.0


    https://www.youtube.com/watch?v=PbpYqUccOd4



    John
    For example 0,7mm and 1,75mm and 2,5mm pitch wouldn't work with your numbers.
    I need 4 different change gears for my imperial Kerry with Norton-style threading gearbox to cover all the metric threads. Even if the leadscrew was metric it would still need some change gears.
    Norton-style quick-change gear box is designed with the imperial pitch sequence in mind but it doesn't work with metric threads nearly as well.

  7. #17
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    Mar 2018
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    Finland
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    Quote Originally Posted by Paul Alciatore View Post
    Ain't math grand.

    Your next revaluation will be that a quick change gear box that was designed for English threads is not ideal for metric ones. Different kinds of sequences. You will need several different manually changed gears to cover the range of metrics.
    Yeah in my lathe this is the situation, I gotta change gears all the time for metric, hardly any better than being without a gear box really, so despite being in metric land I try and keep to TPI threads on my own projects where I make both mating parts.

  8. #18
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    What HopefulDave was sort of saying is that because imperial threads are tpi threads inch and metric are ipt inch (mm) per thread ie the inverse then a Norton type box when driven backwards provides the right sort of ratios for metric. Several industrial lathes eg Harrison M300, larger Colchesters arrange to do that and provide metric or near metric from the same box. The way the old designers managed it probably without CAD simulations and umpteen printed prototypes is impressive.

  9. #19
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    Quote Originally Posted by Baz View Post
    What HopefulDave was sort of saying is that because imperial threads are tpi threads inch and metric are ipt inch (mm) per thread ie the inverse then a Norton type box when driven backwards provides the right sort of ratios for metric. Several industrial lathes eg Harrison M300, larger Colchesters arrange to do that and provide metric or near metric from the same box. The way the old designers managed it probably without CAD simulations and umpteen printed prototypes is impressive.
    AFAIK M300 and other "modern" lathes that are designed with metric threading in mind don't use what would be traditionally considered as a Norton gear box.
    Gearbox design in these is bit more complex

  10. #20
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    SE Texas
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    "A few metric threads are enough. I don't need the others."

    "Just have gearing to use the box backwards."

    "Go digital!"

    There are many solutions.

    I like mine. A full set of manual change gears including a metric transposition gear(s). Not only does this allow metric threads, but with appropriate combinations you can also do things like worms. OK, I have to set up the gear train for any thread, even simple English ones. But I am not in a production situation so a few minutes here and there is not a biggie.

    PS: I like that one where you use the gear box backwards. Neat solution.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

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