SB 13 cutting 12tpi with tumblers set for 16tpi
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  1. #1
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    Default SB 13 cutting 12tpi with tumblers set for 16tpi

    I have a 70's vintage SB 13, just learning to run it. Today I attempted to cut a 16 tpi on a piece of 3/4" cold rolled bar stock. The thread looks good, but it cut 12tpi.
    It has a double tumbler gearbox, & on the plate on it calls for the left tumbler to be in "b", with the right tumbler to be in the first (far left) position. I tried running on the bull great but the threads were really fine.
    Any help greatly appreciated.
    I also posted this in "gunsmithing"
    Thanks

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    Check your gear train under the left hand hinged cover. Maybe some gears switched around. I believe your chart calls out two different gear tooth counts for the A tumbler...

    John

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    Good thread here - also addresses the need for correct use of the several levers on the apron

    13" SB gearing issue

    The most important aspect is that the 24 and 48 tooth gears are ONLY for the STUD position (but not at the same time) , and the 64T is ONLY for the input to QC box position

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    It does, 48 & 24 on the stud gear, have to figure out which is stud gear. Another gentleman replied with a link to a 13 with similar problem, going to take the iPad to the garage and try to figure it out. I looked at the thread and know that I have a 64 tooth on the tumbler input shaft that is being driven.

    I'll post what I figure out.......or more questions.
    Thanks

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    If the the 64 tooth gearbox input gear was replaced with the 48 tooth gear it could be the problem.

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    I think the 64tooth on the gearbox is right, looking at the thread johnoder posted. I took pictures, if i can figure out how to post them.20170616_195026.jpg
    Attached Thumbnails Attached Thumbnails 20170616_195011.jpg  

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    Heres more 20170616_195058.jpg

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    Thanks for the link Johnoder, good read, going to clean up my gears and count teeth over the next few days, have to work tomorrow,
    Many thanks, I'll get back to it in a day or two.

  10. #9
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    Looks like the 127 / 100 metric transposing idler

    I marked your photo for you. Probably is not 24 or 48 teeth

    have to figure out which is stud gear
    ON EDIT:

    Here is the double tumbler HTRAL if needed. Probably more legible to acquire a paper version

    http://campkahler.com/files/How_to_R...he_SB_1of2.pdf
    http://campkahler.com/files/How_to_R...he_SB_2of2.pdf
    Attached Thumbnails Attached Thumbnails 13-sb-gearing.jpg  
    Last edited by johnoder; 06-17-2017 at 06:49 AM.

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    Do you have other gears from the transposition set or the original set?

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    You just need to replace that 34?? tooth gear with your 24 tooth gear.

    You are fortunate as you have the compounded 127/100 metric gears in the idler position...no need to change that, the compounded idler only come into play when you are using the smaller outer 100t outer gear to drive the gearbox.

    BTW- contact Ted about your carriage lock, he may also have the gearing instruction sheet for utilizing the metric capability you have.

    [email protected]

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    Scan thanks to Mr. Wells

    If you had one of these charts you could actually read, you could discern all the various stud gear tooth counts that are involved in cutting metric threads
    Attached Thumbnails Attached Thumbnails sb-double-tumb-metric.jpg  

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    to be clear for your purpose you need the 24T stud on the reverser assembly...see Mr Oders post #9

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    Thanks, I'm pretty sure i have that plate on the gear cover. I counted the teeth on the stud gear that's in use, it has 32 teeth
    I counted the teeth on the other stud gear, don't remember off the top of my head, but I know it wasn't 48 tooth.

    I don't think that i have a 24t gear, looked on ebay this morning, there is one listed, but the lister says it is for a single tumbler machine & wont work on a double tumbler.

    I need to read a lot about this lathe to figure it out, what configuration it is etc.

    Ken, i have no other gears other than what is on the machine.
    I need to clean all of the old grease & gunk off of the gears & count the teeth,

    Anyone have a 24t stud gear that will work on s double tumbler machine?

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    comfirm but I believe this will work...

    24 TOOTH CHANGE GEAR FOR METAL LATHE MACHINE | eBay

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    FYI:
    The standard change gears for the 13" are 14 DP. The Metric transposing gears are 16 DP.
    Ted

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    Hi Ted,
    I'm new to machining, learning as I go. So google is my friend, I looked what DP is and it appears that just changing my stud gear wont work, I'll look up hot to measure dp.
    Im at work right now, wont get home till 5.

    Iwananew10, I'm watching it on ebsy, if it will fit my reversing lever & is a part of the puzzle ill get it.
    I need to read up on this, research dp & how to determine if I need a complete set of gears. If I need a complete set, id rather buy them as a set than piecing the puzzle together with individual gears

    Really appreciate the help from everyone.

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    DP = tooth count + 2 / outside diameter of the gear.

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    Thanks Gadget, I'll check them this evening

  21. #20
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    The Metric transposing gears are 16 DP
    Which says the stud gear installed, reported to be 32 teeth, is 16 DP - since it is engaged with the transposing set

    Which also means that the usual every day (not part of metric rig) stud gear, stated to be 14DP, is not going to be able to use the metric transposing set as an idler


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