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Thread: Let me do it this way:

  1. #1
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    Let me do it this way:

    I have a mid 90's, 13" Central Tool, Taiwanese lathe. When I bought the lathe from an estate conservator, cosmoline was still on most of the machine and it's accessories. That was two years ago. The lathe has a change gear system for thread cutting and speed changes for feed. A problem with this lathe is the half nuts do not always mesh fully, in part because the speed of the lead screw, which is rotating at a very high rate. Consequently, poor engagement sometimes and mebby, not a great set of half nuts, Not sure.

    When I set up to cut threads, I do it by the gears specified in a placard on the belt cover of the machine. The thread pitch always is correct but the lead screw is wailing, always, or pretty much always. There is also a prescribed pattern of lever positions, like 6 of them, just going from memory.

    So, can someone please tell me how I can slow the lead screw down on this machine without interfering with the thread pitch I want to cut?


    Thanks,

    Pete
    Last edited by Pete Wass; 03-03-2019 at 12:56 PM.

  2. #2
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    Pete, the lead screw has to turn the proper amount of revolutions in relation to the spindle speed so that the carriage moves the proper distance in relation to the spindle for what ever thread you are cutting. Thatís how a lathe cuts a specific threads per inch.

    The only way you can slow the lead screw down is to slow the RPM of the spindle down.

    Thatís carved in stone.

    My best advice would be to practice and get to know the personality of your machine. Even I canít just walk up to any machine and figure out itís quirks without first ďgoing through the gearsĒ, so to speak.
    Last edited by jackie schmidt; 03-03-2019 at 02:09 PM.

  3. #3
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    Pete move further back from the start of the cut and whiggle the carriage using the wheel to fully in guage the half nut. If you missed your number its easy to try it again if you have left yourself plenty of room.

  4. #4
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    This may be completely irreverent to your situation but.....

    I useta' cut threads at 70rpms so I'd engage the half-nut about an eighth inch from my work. Because I CAN'T STAND watching the toolbit slowly cross over empty space, makes me wanna' run up to the house and make a pot a' cawffee while the carriage lumbers in.

    Now I thread (manually) at 360 or more rpms and I engage the half-nut 'wayy back from the work. This way it DARTS across the space, and the work, but it gives me lots of time to feel the half-nut settle in. And lots of time to STOP! if the drop feels grungy.

    Don't even have time to take a SIP off the coffee, but lots of time to feel the nut click down.

  5. #5
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    Thanks Jackie

    Quote Originally Posted by jackie schmidt View Post
    Pete, the lead screw has to turn the proper amount of revolutions in relation to the spindle speed so that the carriage moves the proper distance in relation to the spindle for what ever thread you are cutting. Thatís how a lathe cuts a specific threads per inch.

    The only way you can slow the lead screw down is to slow the RPM of the spindle down.

    Thatís carved in stone.

    My best advice would be to practice and get to know the personality of your machine. Even I canít just walk up to any machine and figure out itís quirks without first ďgoing through the gearsĒ, so to speak.
    Somehow I imagined them being two separate systems I guess. I was thinking mebby I had a wrong gear ratio selected that could be slowed down. I couldn't remember if the spindle speed was part of the equation with the set-up on the placard.

    Thanks again,

    Pete

  6. #6
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    Quote Originally Posted by Louis.J View Post
    Pete move further back from the start of the cut and whiggle the carriage using the wheel to fully in guage the half nut. If you missed your number its easy to try it again if you have left yourself plenty of room.
    Can't be done if one is cutting an inverse thread. If one has a brake on their machine they can simply leave the half nut engaged and move anywhere they want to go but when one is tight up against the chuck, there isn't any room or time to do anything. Breaks on lathes are the best invention EVER!
    Last edited by Pete Wass; 03-04-2019 at 02:52 PM.

  7. #7
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    Quote Originally Posted by alinwa View Post
    This may be completely irreverent to your situation but.....

    I useta' cut threads at 70rpms so I'd engage the half-nut about an eighth inch from my work. Because I CAN'T STAND watching the toolbit slowly cross over empty space, makes me wanna' run up to the house and make a pot a' cawffee while the carriage lumbers in.

    Now I thread (manually) at 360 or more rpms and I engage the half-nut 'wayy back from the work. This way it DARTS across the space, and the work, but it gives me lots of time to feel the half-nut settle in. And lots of time to STOP! if the drop feels grungy.

    Don't even have time to take a SIP off the coffee, but lots of time to feel the nut click down.
    WOW! You guys threading barrel tenons, up against a shoulder, threading 16 TPI at 360 RPM?

    Amazing,


    .

  8. #8
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    Yeah! and all these "BREAKS"

  9. #9
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    " WOW! You guys threading barrel tenons, up against a shoulder, threading 16 TPI at 360 RPM "

    ???? What guys I only read one account of an individual being able to do so where did the rest of that group go.

  10. #10
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    Starting to sound like fishing stories.... Iíd like to see videos of guys threading 360 to a shoulder. 90 feels like Iím outta control

  11. #11
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    Jackie Schmidt might have it being shown on one of his few YouTube Videos.

  12. #12
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    How many guys are threading to the shoulder at those speeds with a proximity stop? I was playing with my 1340GT with a proximity stop and it'll stop within .001" when threading at over 250 RPM. Manually disengaging the halfnut I can do around 120 but that's about as fast I can do while still remaining alert.

  13. #13
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    I never had problems with my heavy 10

    Quote Originally Posted by jackie schmidt View Post
    Pete, the lead screw has to turn the proper amount of revolutions in relation to the spindle speed so that the carriage moves the proper distance in relation to the spindle for what ever thread you are cutting. Thatís how a lathe cuts a specific threads per inch.

    The only way you can slow the lead screw down is to slow the RPM of the spindle down.

    Thatís carved in stone.

    My best advice would be to practice and get to know the personality of your machine. Even I canít just walk up to any machine and figure out itís quirks without first ďgoing through the gearsĒ, so to speak.
    Having said that, I'm not sorry I switched lathes but want to get a better grip on why I have had problems with this one.

    So, thinking through this one, If the formula of levers has me in too fast a spindle speed to comfortably do single point threading and I reduce the spindle speed, Will I need to find a different combination of change gears to cut the thread pitch I want?

    Guess I had better wait until I get back home to discuss this more. Too many levers and gears to think about without knowing which goers to where.

    Thanks,

    Pete

  14. #14
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    no
    the gearing stays the same, it happens at a slower speed

    Quote Originally Posted by Pete Wass View Post
    Having said that, I'm not sorry I switched lathes but want to get a better grip on why I have had problems with this one.

    So, thinking through this one, If the formula of levers has me in too fast a spindle speed to comfortably do single point threading and I reduce the spindle speed, Will I need to find a different combination of change gears to cut the thread pitch I want?

    Guess I had better wait until I get back home to discuss this more. Too many levers and gears to think about without knowing which goers to where.

    Thanks,

    Pete

  15. #15
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    Pete the speed does not affect the pitch it remains a constant once its set and this is what Jackie was pointing out. With that being said you have the option to go slower or faster without having to change a single thing in regards to the pitch it will always remain the same.

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