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Thread: Southbend spindle question.

  1. #21
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    Quote Originally Posted by BCRider View Post
    The actual size of the tumbler gears does not matter as long as they are both the same diameter and tooth count. .
    As the tumbler gears are idlers, they don't both have to have the same tooth count. They do not on a Myford ML7. Using different size gears might give more freedom in design if a new tumbler arm is needed.
    Last edited by cameron; 08-12-2019 at 07:58 AM.

  2. #22
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    Quote Originally Posted by cameron View Post
    As the tumbler gears are idlers, they don't both have to have the same tooth count. They do not on a Myford ML7. Using different size gears might give more freedom in design if a new tumbler arm is needed.
    I will try get pics. I guess its not so easy to work out what gears are needed if you change the tooth count of the spindle gear. At least he will have auto feed.

  3. #23
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    Quote Originally Posted by cameron View Post
    As the tumbler gears are idlers, they don't both have to have the same tooth count. They do not on a Myford ML7. Using different size gears might give more freedom in design if a new tumbler arm is needed.
    I had to think a bit about that as there would be a speed change. But since it's a single chain of gears the two on each end would still be the same speed even if the different sizes in the middle run faster or slower. So yeah, I was mistaken about that.

    Quote Originally Posted by plunger View Post
    I will try get pics. I guess its not so easy to work out what gears are needed if you change the tooth count of the spindle gear. At least he will have auto feed.
    You'll still want/need to find the right gear since changing the size of one affects the size needed for the others. Go to the SOUTH BEND PAGE at lathes.co.uk and go down just past 3/4's of the way down the page to where there's a picture of the tumbler and gear drive to the feed screw. You'll see that the tumbler is mounted on a fixed pivot pin and that the diameter of the two tumbling gears just reaches between the gear mounted axially on the tumbler's pivot shaft and the gear on the end of the spindle. Change the size of the gear on the end of the spindle by more than maybe a tooth or two at most and the teeth of the tumbler either won't reach far enough to get a good engagement or the difference will crowd the gap between the two tumbler gears.

    And if you think you can just change the gears of the tumbler that's not as simple either. Change those gear and you will also need to change the small gear that the tumbler set drives or again the teeth won't engage. Or you'd have to change the tumbler gears but then make a new tumbler plate that holds all the new gears in the proper orientation.

    Either way he will have to get gears with the right tooth modulus. And at that point why not just get the right tooth count so the threading table works? If he can't get the proper SB gears but can find the right tooth modulus and tooth number then he can turn the ID to fit. But it would be a real headache to try to use gears with different tooth counts in that fixed size design of the tumbler train.

  4. #24
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    I visited my mate today with my camera. We have many more questions. But I could not take pics of the spindle as he took it to an engineering firm and they will braze it up and recut the gear for $60.Hopefully it has a happy ending.

  5. #25
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    That sounds like a VERY fair price by any standards ! ! ! !

    That's more time now to work on cleaning up and checking out the rest of the machine. I hope the rest goes more smoothly for you and him. They are great smaller size lathes and seeing one is abused condition is not far off looking at a beaten puppy....

  6. #26
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    I am curious to know if the tailstock on original southbends is a left hand thread. I see this tailstock is a right hand thread .In order to drill you need to wind anticlockwize.

  7. #27
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    When I first got my SB-9 I had to disassemble the headstock to install a new belt (serpentine belt with no splice). When I did I discovered that the felt oilers had completely worn down, exposing the end of the spring to the bearing surface of the rotating spindle. This produced scratches in the spindle at the points where the oilers rode on it. They were not real bad, actually less than what an oil groove would be and after careful inspection for any burrs, I concluded that they did not need any further repairs. The oilers were still available from SB so I purchased a pair and replaced them. It has run fine since then, but it is in a home shop where the use is occasional, not a commercial shop where the use would be a lot more.

    I did a photo of the new oilers so others can construct them if obtaining them is difficult.



    The gear on the spindle of my lathe is also machined into the spindle itself and can not be changed. It has worn teeth, probably from a lack of the proper DAILY lubrication that it should have gotten and keeping the gear train engaged all the time. This wear is even on all of the teeth and mostly produces a lot of backlash. But when I use the gearing for cutting or threading the cutting forces keep the gears in mesh and the backlash is not a concern. A new spindle would be nice, but not essential. I am living with it.



    Quote Originally Posted by plunger View Post
    My mate removed the spindle and informs me there is damage to the spindle bearings as well as headstock journals.But google tells me this looks worse than it is in reality. I dont know if this is true. I will get pics soon.There were no wicks to both the bearings.With regards to the gear on the spindle its not one or two teeth damaged but most.
    Thats why i was wondering if the entire gear cant be machined off and a bigger gear made that keys to the back of the spindle. It will throw the meshing out but it seems there is some sort of tumbler that shares two exact same size gears. If these two gears could be changed to smaller gears could it not be a simpler way.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

  8. #28
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    Quote Originally Posted by plunger View Post
    I visited my mate today with my camera. We have many more questions. But I could not take pics of the spindle as he took it to an engineering firm and they will braze it up and recut the gear for $60.Hopefully it has a happy ending.
    That is an excellent price and a good solution to the problem. Now his speed and threading charts will work also. Hopefully the rest of the job goes easier -- they are rugged lathes, but often abused. EDIT the tail stock -- I have never heard of a south bend going anti-clockwise. This makes me think it is not the correct tail stock, or if it is, then somebody has done a poor repair on it.
    Last edited by nickel-city-fab; 08-12-2019 at 04:18 PM.

  9. #29
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    RE: That tumbler reverse thing

    The gears of the tumbler reverse are in fact idlers and only act as such. They transfer the motion on a tooth-by-tooth basis and have absolutely no effect on the gear ratio for the purpose of cutting threads. And the two gears of the tumbler reverse do not need to have the same tooth count. They are probably chosen for their ability to fit in the space available and to alternately mesh with the spindle gear with a bit of dead space between those two meshes so there is never any conflict. So, these tumbler reverse gears could be changed to any other tooth counts with no effect on the gear ratio.

    Now, my SB has what is called a stud shaft. This stud shaft is at the rotational axis of the tumbler reverse bracket and has a gear with the same tooth count as the spindle gear. It is in mesh with the second gear of the tumbler reverse. So it is also connected to the gear train as an idler gear would be. So, the gear on the stud and the stud itself rotates in lock step with the spindle due to the fact that they have the same number of teeth and have only true idlers (tumbler reverse gears) between them. This "bottom" gear on the stud is not designed to be changed: it's job is to run in step with the spindle. A second, outer gear on this stud gear is the start of the changeable gear train for threading purposes.

    So, if you are going to replace the spindle gear with a larger one with a higher tooth count, the logical thing to do would be to first replace that fixed, "bottom" gear on the stud with one that has a matching tooth count. And then replace the two tumbler reverse gears with ones that have a tooth count that allows them to fit. This would preserve all gear arrangements from the stud to the lead screw. This would work with both manual change gear lathes and ones with a quick change gear box. All the changeable gearing would remain the same. The difficulty with this will be getting the tumbler reverse gears to fit. The new ones would probably have lower tooth counts and a new bracket for them may be needed.

    Another thing that could be considered is using a different, perhaps finer, pitch on these four gears: the spindle, the two tumbler reverse, and the fixed gear on the stud. Since these four gears only mesh with each other and not with the gears that are further down the gear train, they can be of any convenient pitch. This would also preserve all of the existing gearing from the top of the stud to the lead screw for both manual gear lathes and ones with a quick change box. This approach may allow you to find gears which will fit on the original tumbler reverse bracket.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

  10. #30

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    Wow, now why go to all this bother and trouble, with a totally worn out Boat Anchor ?

    Unless your getting this lump of worn out scrap metal for free, why even bother with repairing this outdated piece of crud ?

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