4 ms·

For anyone who isn't aware: that's the pair of gears with the smallest number of teeth (and by extension, largest teeth for a given size pair of gears) in the r

For anyone who isn't aware: that's the pair of gears with the smallest number of teeth (and by extension, largest teeth for a given size pair of gears) in the ratio of 2.54:1. As I'm not a machinist, I'm not going to try to explain just where in the geartrain you'd use this pair to convert your metric machine lathe into a US customary lathe, but that's what they're for.

analog31 2y ago
There's typically a gear train that communicates the rotation of the spindle to the threading mechanism. This is so that you can turn a precise number of threads per unit length, and to take multiple passes to reach the desired thread depth. There's a multi-ratio gearbox that sets the thread pitch. The 2.54 ratio lets you turn metric threads on a US machine, with the help of tables in the manual for how to set all of the levers. Machinists hate it, and these days will prefer to buy a die for the occasional threading job.
- mikewarot 2y ago
  I think if I had to do metric threads often, I'd switch to an electronic leadscrew, like the one from Clough42.[1] [1] https://github.com/clough42/electronic-leadscrew/wiki https://github.com/clough42/electronic-leadscrew/wiki
- mauvehaus 2y ago
  The remaining problem is that metric threads are specified by the mm between peaks, whereas US customary threads are specified by threads/inch. It's not immediately obvious to me (not a machinist) that the 127/50 ratio gets you the ability to cut metric threads without a mess of other head-scratching because you're now dealing with period instead of frequency.
  - analog31 2y ago
    Indeed, the charts for cutting metric threads are complex, and I'm not sure all of the standard pitches are even possible. The lathe that I use hasn't had its threading gears installed in ages. A weird historical tidbit is that after WWII a couple of standards emerged for bicycle parts in Europe, where they used metric diameters and inch thread pitches.
    - mauvehaus 2y ago
      The Italian bottom bracket threading standard is completely insane. Like, how do you even cut that, and why would anyone come up with that in preference to literally anything else?
      - analog31 2y ago
        The only thing I can imagine was a supply of American machine tools from the rebuilding of Europe after a WWII. You can always cut any diameter, only the thread pitches are ruled by the capabilities of the lathe. Also, left handed threads involve their own issues since the spindle chuck wants to unscrew itself.

analog31 2y ago

There's typically a gear train that communicates the rotation of the spindle to the threading mechanism. This is so that you can turn a precise number of threads per unit length, and to take multiple passes to reach the desired thread depth. There's a multi-ratio gearbox that sets the thread pitch. The 2.54 ratio lets you turn metric threads on a US machine, with the help of tables in the manual for how to set all of the levers. Machinists hate it, and these days will prefer to buy a die for the occasional threading job.

mikewarot 2y ago
I think if I had to do metric threads often, I'd switch to an electronic leadscrew, like the one from Clough42.[1] [1] https://github.com/clough42/electronic-leadscrew/wiki https://github.com/clough42/electronic-leadscrew/wiki
mauvehaus 2y ago
The remaining problem is that metric threads are specified by the mm between peaks, whereas US customary threads are specified by threads/inch. It's not immediately obvious to me (not a machinist) that the 127/50 ratio gets you the ability to cut metric threads without a mess of other head-scratching because you're now dealing with period instead of frequency.
- analog31 2y ago
  Indeed, the charts for cutting metric threads are complex, and I'm not sure all of the standard pitches are even possible. The lathe that I use hasn't had its threading gears installed in ages. A weird historical tidbit is that after WWII a couple of standards emerged for bicycle parts in Europe, where they used metric diameters and inch thread pitches.
  - mauvehaus 2y ago
    The Italian bottom bracket threading standard is completely insane. Like, how do you even cut that, and why would anyone come up with that in preference to literally anything else?
    - analog31 2y ago
      The only thing I can imagine was a supply of American machine tools from the rebuilding of Europe after a WWII. You can always cut any diameter, only the thread pitches are ruled by the capabilities of the lathe. Also, left handed threads involve their own issues since the spindle chuck wants to unscrew itself.