South Bend 10 Bi Tumbler Metric Thread Question
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  1. #1
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    Default South Bend 10 Bi Tumbler Metric Thread Question

    img_20200214_154217312.jpg
    I'm sure the information I need is on this site but I cannot find it.
    I'm trying to get my ducks in a row to finish a project tomorrow.
    For the first time I am trying to turn an external metric thread.
    I have swapped the gears as the gear chart suggest.
    For 1mm thread pitch the thread gear chart says;
    Plunger Hole - C
    Then it says ;
    Plunger Hole - 1
    Could someone tell me if Plunger Hole 1 is the the same as "A-4" in Feeds?dsc03933.jpg
    Sorry, best pic I could post.
    In other words, in feeds, are they referring to the top left hole?
    Thank you very much ahead of time if some one has the time.
    Michael

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    On any thread you start cutting, try to get a scratch of thread pitch in the O.D. before it's at final size on the O.D. Then you can measure it and verify your settings. If there is room for 11 revolutions of thread-pitch-scratch, you'd have 10MM from 1st scratch to the 11th (10 spaces between scratches at 1MM each).

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    When setting up a SB inch lathe to cut a metric pitch you must perform a two step process. First reference the gear transposing chart. Then find your desired pitch on the left column. Then follow to the right on that chart line and you will see first the correct stud gear selection then the correct handle positions for the quick change gear box. In your case, you need the 32 tooth stud gear as the first step. Then set the quick change gearbox as the second and last step, where the left lever is positioned in the "C" hole and the second lever is positioned in the "1" hole. You may know this, but if you don't, please note that once you engage the half nut on the apron, you must not disengage the haft nut until the thread is complete. You cannot use the inch thread dial and at the end of every pass the lathe must be stopped, the tool withdrawn and the lathe reversed so the carriage returns well past the thread start point to eliminate any backlash. Then the carriage feed is returned to the "0" point and the tool advanced with the compound for the next cut. Lastly, the lathe motor is turned back on. This process is then repeated until completion of the thread. This makes you really wish you had a spindle brake, but that is how it is done.

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    Quote Originally Posted by steve-l View Post
    You may know this, but if you don't, please note that once you engage the half nut on the apron, you must not disengage the haft nut until the thread is complete. You cannot use the inch thread dial and at the end of every pass the lathe must be stopped, the tool withdrawn and the lathe reversed so the carriage returns well past the thread start point to eliminate any backlash. Then the carriage feed is returned to the "0" point and the tool advanced with the compound for the next cut. Lastly, the lathe motor is turned back on. This process is then repeated until completion of the thread. This makes you really wish you had a spindle brake, but that is how it is done.
    Not a "hard" rule and with a little practice, it is as easy to do as SAE threads. Here's a video on how to do it just like inch threads:


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    WOW!
    I got up Sat morning and started reading out loud to my wife all the help here and we started to cry.
    This info was very needed and it is so to the point. Thanks you all!
    I went to the shop and put this info to work. SUCCESS was had. I had one pass that sort of split my thread but this is a one time tools and it will work great.
    I will try to post some pics and maybe a short video.
    Michael

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    Some excitement;
    img_20200215_123712137.jpg
    img_20200215_114734988.jpg
    img_20200215_114726541.jpg

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    More excitement!

    Happy Days!

    The pipe wrench marks are from when I had done this the first time with 1/2x24tpi.
    I had the 2 parts together and apart several times and then I decided to clean with carb cleaner and ran together when it galled. I mean GALLED! Trying to unscrew with pipe wrench until broke off and that was the need for 14mm x 1mm thread pitch so the rest of the project would work.
    The next step was in the indexer so I could create 3 feet on the bottom but part slipped in indexer and messed up my measuring and next thing I knew it is junk.
    Well, I can save it but will be easier and quicker to start over.


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