Bizarre lathe vibration
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  1. #1
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    Default Bizarre lathe vibration

    I have a really strange vibration problem with my Bulgarian ZMM lathe. It's a great machine which I've used for over 18 years, however it has slowly developed a vibration in one gear. This is where it gets weird: If I reverse the motor (3 phase) and put the machine in reverse (so the spindle still rotates correctly) the machine is as smooth as silk! Really can't get my head around this, obviously I need to have a look in the headstock but finding time in my busy shop is a problem.
    Any ideas?

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    Quote Originally Posted by Tony McPhee View Post
    I have a really strange vibration problem with my Bulgarian ZMM lathe. It's a great machine which I've used for over 18 years, however it has slowly developed a vibration in one gear. This is where it gets weird: If I reverse the motor (3 phase) and put the machine in reverse (so the spindle still rotates correctly) the machine is as smooth as silk! Really can't get my head around this, obviously I need to have a look in the headstock but finding time in my busy shop is a problem.
    Any ideas?
    .
    i had a lathe i had hand tapped a 1.5" 12tpi thread on and had lathe headstock locked. the force required damaged the pin in gear holding headstock from turning. using a 18" wrench on the tap was not a good ideal
    .
    gears probably damaged

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    Booting off previous post -
    In your "reverse and reverse" configuration, is there a gear which is not used but which is used in the "forward and forward" arrangement? Might be a clue.
    Good luck,
    Monoblanco

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    I think Monoblanco nails it. The reverse tumbler has two gears. One drives while the other idles. If the only difference is the motor in reverse and the reverse tumbler in reverse, my guess would be a bad gear (or maybe just a chip caught in the gear that is idling in reverse).

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    FWIW I had a W&S #3 that had a slightly twisted bed when I bought it. It also shook at one speed. I got the bed straight by twisting it straight by bolting it to the floor. After a few years the shake when away, and the bed no longer sprang back when unbolted from the floor. Makes no sense, but neither does yours. I can't say this has any relevance to your machine, but just maybe the leveling of your machine deserves a look after 18 years.

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    Quote Originally Posted by Dumpster_diving View Post
    I think Monoblanco nails it. The reverse tumbler has two gears. One drives while the other idles. If the only difference is the motor in reverse and the reverse tumbler in reverse, my guess would be a bad gear (or maybe just a chip caught in the gear that is idling in reverse).
    Thanks guys, my guess is a damaged tooth as this speed gets used a lot. The lathe has a clutch for forward/reverse, not sure how reverse works as I haven't had the cover off the headstock for years. I suspect the driving flank of the teeth on the gear concerned must be worn as it only affects this one speed roughly in the middle of the range.

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    Quote Originally Posted by Mud View Post
    FWIW I had a W&S #3 that had a slightly twisted bed when I bought it. It also shook at one speed. I got the bed straight by twisting it straight by bolting it to the floor. After a few years the shake when away, and the bed no longer sprang back when unbolted from the floor. Makes no sense, but neither does yours. I can't say this has any relevance to your machine, but just maybe the leveling of your machine deserves a look after 18 years.
    I moved the machine about 6 months ago and leveled it again, no change!

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    My old Colchester was 'smooth quiet' in high gear reverse. In high gear forward, it was smooth but noisier by a lot. I had the gearbox cover off, no broken teeth or anything else that looked bad. I always assumed it was 'the bearing' though it also looked good.

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    If the motor reverses though unit contactors ,check the forward contactors for burned contacts.,or maybe a problem in the contactor solenoid or coil.Sometimes they "growl"....Worn gears usually make a lot of noise before any vibration would be felt.....also check for a worn shaft /loose pulley /key/on the motor.

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    Quote Originally Posted by GregSY View Post
    My old Colchester was 'smooth quiet' in high gear reverse. In high gear forward, it was smooth but noisier by a lot. I had the gearbox cover off, no broken teeth or anything else that looked bad.
    Most likely tooth wear. They look fine but the shape has worn enough so that the teeth bang when they engage. Just a little bang but thousands of times a minute ...

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    If you take the head cover off and find helical gears in there maybe one in the train that set uses is changing its thrust direction when you swap things around.It may be rubbing one way and moving away from the interference the other.A loose shaft locking collar will let it float back and forth.

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