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  1. #11
    barryjyoung's Avatar
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    Hi Clayton, yes, I an cut 25 tpi.




    Quote Originally Posted by claytume
    Can you guys with lathes cut 25tpi?

    I don't have a job for you but many years ago I was asked to make adaptors for lens cells into a shutter, 25tpi.........couldn't do it and never seen a lathe that had that pitch on it.

    Clayton
    Barry Young
    Young Camera Company

  2. #12

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    I checked my (very old) lathe. 24 and 26 tpi, no 25. Don't have the change gears to cut 25. Sorry.

  3. #13
    Donald Qualls's Avatar
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    Quote Originally Posted by claytume
    Can you guys with lathes cut 25tpi?

    I don't have a job for you but many years ago I was asked to make adaptors for lens cells into a shutter, 25tpi.........couldn't do it and never seen a lathe that had that pitch on it.
    I'm pretty certain my lathe, with 16 TPI lead screw, can do this if I have the right gears (or order some inexpensive spares) for the change gear train. If I haven't bent my brain, I'd need 50:20 compounded to 50:80, but I don't think the original change gear set includes two 50 tooth gears. It'd be dead simple on a larger lathe with the very common 10 TPI screw, if it's got manual change gears, just a 20:50 or equivalent pair and enough no-change to complete the train.

    It's very common, however, to find lathes with quick-change gearboxes for which there either doesn't exist a manual change train, or more likely the manual gears were put away years ago and no one now in the shop has ever seen them. Since 25 TPI isn't a standard thread, it's not found in most QC boxes.

    The most modern of the small lathes have "electronic lead screws" using shaft encoders on the spindle, counter/divider systems, and stepper motors driving the lead screw, to cut any thread, either metric or inch, that you can specify -- right or left hand, front or rear tool post, inside or outside. Need to cut a 28.6 tpi to match some bizarre non-metric thread found on something? No problem...
    Photography has always fascinated me -- as a child, simply for the magic of capturing an image onto glossy paper with a little box, but as an adult because of the unique juxtaposition of science and art -- the physics of optics, the mechanics of the camera, the chemistry of film and developer, alongside the art in seeing, composing, exposing, processing and printing.

  4. #14

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    Quote Originally Posted by Donald Qualls
    The most modern of the small lathes have "electronic lead screws" using shaft encoders on the spindle, counter/divider systems, and stepper motors driving the lead screw, to cut any thread, either metric or inch, that you can specify -- right or left hand, front or rear tool post, inside or outside. Need to cut a 28.6 tpi to match some bizarre non-metric thread found on something? No problem...
    Donald..........never seen or heard of these.........anywhere on the net I can see one?

    Clayton

  5. #15

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    Quote Originally Posted by Donald Qualls
    It's very common, however, to find lathes with quick-change gearboxes for which there either doesn't exist a manual change train, or more likely the manual gears were put away years ago and no one now in the shop has ever seen them. Since 25 TPI isn't a standard thread, it's not found in most QC boxes.
    Yes the lathe I had access to had a QC box and no change gears. The shutter was a #5, can't remember the brand. Seemed very odd to me at the time a 25 tpi thread, never seen another one.

    Clayton

  6. #16

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    In a pinch, one could probably get away with using a 1.0 thread to fit a 25 TPI. As long as the length of the threaded section is short enough to avoid jamming and the thread was cut loose.

    If you take the decimal equivilent of 25TPI (1/25 = .04), it is nearly the same as a 1.0M pitch (1.0/25.4 = .0394"). Granted, it is best to use the right thread. And as Donald pointed out, there are lathes today which use the "electronic lead screws" which make machining the right threads a dream.

    Adam Dau

  7. #17
    Ed Sukach's Avatar
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    Quote Originally Posted by claytume
    Can you guys with lathes cut 25tpi?
    I don't have a job for you but many years ago I was asked to make adaptors for lens cells into a shutter, 25tpi.........couldn't do it and never seen a lathe that had that pitch on it.
    I can't ever remember coming across a 25 T.P.I. thread. I wonder,

    1) How was the pitch determined? ... by measurement or ? If someone used the folding "Thread Pitch Gages", they might well mistake a 1 millimeter pitch for ...? Then again, I can't ever remember seeing a folding thread pitch gauge (National Thread Form) with a 25 T.P.I leaf.

    2) Is it possible that the thread in question had something other than a 60 degree National/ Metric form? I don't know ... but it might have been something like a Whitworth (55 degree rounded) or Lowenhertz 53 degrees, 30 minutes; or -- or Dardelet Self-Locking ... or ..... I don't know what the "standard" pitches were for those.
    Carpe erratum!!

    Ed Sukach, FFP.

  8. #18

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    Quote Originally Posted by S.K. Grimes
    In a pinch, one could probably get away with using a 1.0 thread to fit a 25 TPI. As long as the length of the threaded section is short enough to avoid jamming and the thread was cut loose.

    If you take the decimal equivilent of 25TPI (1/25 = .04), it is nearly the same as a 1.0M pitch (1.0/25.4 = .0394"). Granted, it is best to use the right thread. And as Donald pointed out, there are lathes today which use the "electronic lead screws" which make machining the right threads a dream.

    Adam Dau
    Yes I thought of that one, would work like you say if the thread was cut loose and was very short.

    Clayton

  9. #19

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    Quote Originally Posted by Ed Sukach
    I can't ever remember coming across a 25 T.P.I. thread. I wonder,

    1) How was the pitch determined? ... by measurement or ? If someone used the folding "Thread Pitch Gages", they might well mistake a 1 millimeter pitch for ...? Then again, I can't ever remember seeing a folding thread pitch gauge (National Thread Form) with a 25 T.P.I leaf.
    Was measured with screw pitch gauges, both metric and imperial......yep I've never seen one before either.

    Clayton

  10. #20
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    25 tpi is used on many old wood working tools to make the screws proprietary. The biggest offender by far was Stanley Tool Works. I made a living for a few months making replacement screws for the venerable old Stanley #45 and #55 combination planes. I suspect that this thread may be oddball for similar reasons.


    I had to do the math on my change gears in order to turn 25 tpi. Almost all lathes with screwcutting ability can be used to make oddball threads that are not listed on the change gear charts. It is a matter of fractions. If you have a 16 tpi leadscrew then the fraction is 16/25 or .64 turns of the leadscrew for each turn of the spindle. Not many 16 tooth change gears out there, so multiply the fraction by two to get 32/50. Those gears I have. Engage a 32 tooth gear with the bull gear on the spindle and slap a 50 on the end of the leadscrew. Use an idler gear of any size to hook them together and you have 25tpi. You can get some really odd pitches this way. Just remember that gear ratios are merely fractions, maintain the relationship between the numerator and denominator and you will be fine. This also works with compound gearing which is where you can get some incredibly odd pitches. How about 114.6 tpi? Hmmm??? Multiply the possibilities immensely if you have a quick change gearbox on the leadscrew.

    For an excellent dissertation on figuring out your own change gear combos, I recommend Using the Small Lathe by L.C. Mason. It is published by Tee Publications in England
    Barry Young
    Young Camera Company

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