Hendey T&G Metric threading
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  1. #1
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    Default Hendey T&G Metric threading

    hendey-t-g-threads-feeds.jpg


    Some are confused by "gear feed in thousands" in that table. 100 tpi is 10 thousands feed. What am I missing?

    I had to think about this. It does seem confusing.
    The OUTPUT of the Norton box is
    either to a Leadscrew (and then to the half nuts)
    or to the Feedrod (and then to the feed clutch lever).
    So if you divide it out, the Feedrod moves the carriage
    4.167 times slower than the Leadscrew. So that is where
    those feed numbers per rev come from.

    Now the other thing the chart says is
    Belt feeds equal one-half of Gear feeds.
    This is because the INPUT to the Norton box is
    selectable through the change gears from the spindle
    OR a Vee belt coming from the spindle. So the belt
    feed ratio is 1/2 the change gears feed ratio.

    I once had a thought to replace the Vee belt with
    a tooth timing belt and pulleys, so it would not slip.
    That way you could cut threads twice as fine as
    indicated on the chart. But 240 tpi might be useless.
    The Hendey T&G lathe is an amazing machine.


    So don't forget, the feedrod is 4.167 times slower,
    so 120 tpi (in threading terms) becomes 500 tpi (in threading terms).
    Change the input to the Norton box from gears to belt,
    and that gets cut in half again, so the finest feed on the Hendey
    becomes 1000 tpi (in threading terms) or .001" per rev.
    Make some diffraction gratings anyone ?

    So can one cut metric threads with the factory
    Hendey Norton gearbox with the 24:48 (1:2)change gears ?



    1mm would be double 13 tpi, or 26 tpi in this case.
    So 6-1/2 tpi would be equivalent to 4mm pitch.





    So my math is

    1" / 13 tpi = .077" pitch

    2mm / 25.4 = .079" pitch


    --------------------------


    1" / 26 tpi = .039" pitch

    1mm / 25.4 = .039" pitch


    ----------------------------


    1" / 6.5 tpi = .154" pitch

    4mm / 25.4 = .157" pitch

    ------------------------------


    1" / 17 tpi = .059" pitch (my Hendey doesn't have that one)

    1.5mm / 25.4 = .059" pitch

    A workaround is to set the Norton box to 4 tpi, and select the
    feed rod (not the leadscrew), which gives...

    1" / 4 tpi = .25" pitch
    .25" / 4.167 (feedrod reduction factor) = .060" pitch

    This works by leaving the bed feed clutch engaged
    and reversing the spindle to rewind each threading pass,
    because you are feeding with the rack, not the leadscrew.

    ----------------------------------


    1" / 20 tpi = .050" pitch

    1.25 mm / 25.4 = .049" pitch


    ------------------------------


    1" / 14 tpi = .071" pitch

    1.75mm / 25.4 = .069" pitch





    -Doozer

  2. #2
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    Default

    This is an interesting idea. I had never considered that the T&G has so many feed rates that you could possibly get close enough to do metric as well.

    However, I'm not really convinced that, for example, a 26 tpi nut will thread onto a 25.4 tpi bolt. Sure the pitch is close, but is it close enough?

    Maybe when you replace the belt with a toothed timing belt, you should use a 100/127 tooth sprocket pair. Or gears maybe? Then just flip a lever and have real metric feeds.

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    1" / 26 tpi = .038" pitch
    1" / 25.4 tpi = .039" pitch

    So one thousandth is not close enough,
    as per your example ? Just asking.

    -Doozer

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    Quote Originally Posted by jwearing View Post
    ...Maybe when you replace the belt with a toothed timing belt, you should use a 100/127 tooth sprocket pair. Or gears maybe? Then just flip a lever and have real metric feeds.
    Yes I was thinking about that. Seems like a great idea.

    -D

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    Quote Originally Posted by Doozer View Post
    1" / 26 tpi = .038" pitch
    1" / 25.4 tpi = .039" pitch

    So one thousandth is not close enough,
    as per your example ? Just asking.

    -Doozer
    That doesn't sound like much, but a normal nut has what, 5 threads? So the offset between the first and last thread will be more like .005". That seems like it would be at least a tight fit.

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    This might only be a problem
    if the nuts thread pitch diameter
    and the bolts thread pitch diameter
    are the same, which they never are.
    (I love reading about thread in the
    Machinery Handbook, call me crazy).
    There is clearance in there.
    It is actually a slight benefit for
    strength to have some mismatch in the
    thread pitches. Look up asymmetrical
    thread profile. Theory is as the first
    threads that are engaged take the tensile
    load, the material deflects some, and
    progressively more threads then begin to
    take the tensile load. If you have
    conventionally cut threads, all the
    threads that are in engagement take the
    load at the same time, and as the bolt
    stretches, it only stretches at the point
    where it enters the nut. With asymmetric
    thread geometry, it spreads the bolt stretch
    throughout the length of the nut.
    Similar concept is used to create uniform
    roller chain loading by running the chain on
    nylon sprockets. The gullets of the nylon
    teeth deflect, and the tight and stretching
    chain applied its load to more than one
    sprocket tooth.

    -Doozer


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