South Bend 9B auto feed and change gear question
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  1. #1
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    Default South Bend 9B auto feed and change gear question

    I have recently acquired a South Bend 9b. I have just went through and rebuilt the entire lathe and everything is working so far. My one issue is the change gears. When I put it back together, I reinstalled the gears that were already on it. From the thread chart it shows to be 20tpi. I had a piece of aluminium that I chucked up just to test things out, and when I use the auto feed it seems to be trying to cut threads instead of turning. This is using the clutch not half nuts. Is there a specific gear setup that I need to use if I am not cutting threads. I have tried searching for information on the change gear system but keep coming up with converting to a qcgb or people missing gears. I did find a manual and it just says you can obtain a wide range of auto power feed by changing the gears the same as with threading.

    I have all the gears that came with the lathe. This is also the first lathe I have touched but familiarized myself with everything before I picked it up so I knew what I was getting.

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    .017" is quite a coarse feed rate and may visually look like a thread.

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    The power feed drive is a bit more than 3:1, so you are currently cutting a 60ish TPI thread with the power feed. That will definitely be visible. Sounds like you just need to change to a finer threading gear.

    The general rule is small gear drives big gear to go finer. Eventually there will be a limit to how far you can go, so then you introduce a compound gear. The same basic rule still applies, you just do it twice- small stud gear drives the big side of the compound, small side of the compound drives the big leadscrew gear.

    allan

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    Since you say you have a complete set of gears and a chart, you have no problem! Pay no attention to the threads/in. numbers on the chart unless you are threading, for feeds, use the feed/rev numbers. Set up the gearing for something between .003" to .006" per rev, that should be a good place to start on that machine. Adjust the feed up or down from there as needed, but without a QCGB, I usually set the machine for a compromise between roughing and finishing feed rates and leave it there, unless I'll will be doing a lot of one or the other.

  5. #5
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    You DO have to use the feed clutch knob and NOT the half nut lever

    The three position lever has to not be in the middle hole

    Thumbnail is chart if needed - way down to bottom is the FEEDS area
    Attached Thumbnails Attached Thumbnails sb-9-b-chart.jpg  

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    A lathe cut /turn with a sharp point bit will look line a thread and is actually that with each pass making a new thread.. a radius point will make the cut /turn look more smooth but will still be a scalp of the radius. A finish pass with no cross feed may/will blend the cuts to look smoother..feeding less than .010 per rev with perhaps .020 radius will give an OK surface finish. feeding perhaps .003 per rev of the part even better.

    Consider at .010 feed per rev that is like a 100 thread per inch thread.
    One inch divided by .017 = 58.8 so is about a 60 thread per inch (at kitno said in post #3)

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    Thank you all for the replies. I wasn't understanding the chart when looking at it for feed speeds. Now I do. Thanks again.


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