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Thread: Southbend spindle question.

  1. #11
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    Repair is possible, or even replace it with another gear. I would bet that a motorcycle transmission would have some good gears in that size range. BTW, many of the South Bend lathes had plain cast iron bearings, and the spindles were finished mirror smooth. Proper oiling is essential.

  2. #12
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    The reason the gear in question is machined into the spindle itself is to get to minimum size however the changewheel gearing doesn't start until after the tumbler reverse. So you can turn off the teeth and shrink or locktight but not anything hot and larger one on. Then either allow for it in the thread calculations or make the input gear to the tumbler reverse match it.

  3. #13
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    I dont quite understand the tumbler as its not in front of me but do they actually effect the gear train ratio.Could any gear here not be used .Isnt it more like an idler gear ,just changing direction.I tried looking on southbend group but could not find a repair for this either.

    I did find an interesting line bore thread though.The guy line bores using the lathe bed itself and a steady rest. He then machines a p bronze bush/bearing.

  4. #14
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    Yeah, the tumbler is just two gears of the same size. But without modifications to the tumbler's frame you can't switch them. The tumbler arm is designed to let the tumbler gears engage with the gear on the end of the spindle. And that means that the tumbler swing axis is set at a specific radius to allow the tumbler gears to engage the gear on the spindle and the gear train below that. So you'll find that you're pretty well stuck with using the proper gears.

  5. #15
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    As long as you use the same number of teeth on the end of the spindle then nothing else needs to change

  6. #16
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    Quote Originally Posted by nickel-city-fab View Post
    As long as you use the same number of teeth on the end of the spindle then nothing else needs to change
    I would think to make a gear that could be locktited to the spindle I would have to machine the damaged gear off . Then the gear would have to have more teeth than the original gear. It looks like the root?(deepest part ) of the gear is exactly the same as the od of the spindle.If I make a gear with more teeth the gear would be bigger than the original.So if I use two smaller tumbler gears but adapt the tumbler so the gears mesh would this not work.?
    If this spindle gear was brazed with silicone bronze is there a chance it could cause the spindle to warp?

  7. #17
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    Two smaller gears would work. I have seen guys braze them up with silicon bronze with no problems also. Larger models had a separate gear that could be removed. Or, you could make one the same as the original, and press it onto a sleeve in the end of the spindle. Have seen that done, too but you lose some internal diameter that way.

  8. #18
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    The actual size of the tumbler gears does not matter as long as they are both the same diameter and tooth count. They serve as an idler in one direction where only one gear is running between the spindle and gear train and in the other mode as a matching pair to reverse the rotation without altering the ratio.

    But they mount to a lever arm that swings in such a way and with mounts that it is expecting a given size of gear to be there. So you need the same tooth pitch and tooth number as the originals or you won't match up to the gear on the end of the spindle. The other gears are not as critical since those in the lower train are all on slots and can be set up to compensate. But the spindle end gear and the two tumblers need to be as specified or they won't engage.

    Of course anything is possible if you're willing to venture into additional modifications. Shifting the pivots of the tumbler arm could compensate for different tooth number gears. But how far does one need to go for getting the lathe back into operation? Also given that there's a good world availability for NOS and reproduction parts for the SB 9 inch lathes.

  9. #19
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    Its too bad you can't use eBay, new spindles are easily available, at least in the US. Sometimes you can find the entire headstock for as little as $100.

    In your situation, I would seriously consider brazing it up and cutting new teeth into the brass, using the tumbler gears for a pattern. If you are worried about it warping, consider hanging the spindle vertically, with the chuck end up and the gear end down, while you are brazing it -- gravity will tend to pull the spindle straight while you are brazing.

  10. #20
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    Curious how a previous owner managed to wreck this gear so thoroughly, if its part of the spindle then its good quality steel, without totally destroying the rest of the gear train as well. Photos would help.
    'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

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