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Thread: Help on a 13"

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    Default Help on a 13"

    Hi all,

    First time posting here so please bear with me

    I've owned my 13" for over twenty years now and for the first time I need to cut a metric thread. It's a bog standard 13" toolroom lathe with 6' bed and an English (8TPI) leadscrew. The Cat No. is CL8145C, SERIAL 152 01286. (not sure what year it was made). It has a dual tumbler gearbox. The current gearing is standard , a 24/48T stud , 80T idler , 64T gearbox drive.img_20190629_154231.jpgimg_20190629_154231.jpg

    I've done as much research as I can but I just can't afford a full metric conversion kit. So, I was wondering if I could compound a 63T spur gear with the 80T idler and use that to drive the 64T gearbox drive. It would all seem to fit in and there's enough adjustment on the banjo to be able to do it (a 63T is about 4.5" OD). I've measured the existing gearset and seems to be a bit of an unusual pitch (DP14).

    By Compounding A 63T with the 80T I get a ratio of 1.269. Is that close enough? I only have a thread length of 2" to cut at 1mm pitch.

    If this looks okay can anyone suggest a source for an 63T spur gear with a 14.5 PA?

    Oh. Also what will happen regarding my thread dial?

    Cheersimg_20190629_154205.jpgimg_20190629_154400.jpgimg_20190629_154400.jpgimg_20190629_154400.jpgimg_20190629_154140.jpg
    Last edited by Westie; 06-30-2019 at 12:25 PM. Reason: Add pix

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    Pressure angle is 14 1/2 degrees
    The standard idler gear has 80 teeth.
    Ted

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    Quote Originally Posted by SBLatheman View Post
    Pressure angle is 14 1/2 degrees
    The standard idler gear has 80 teeth.
    Ted
    Thanks Ted, just counted instead of looking at the casting which looks for all the world like 69T, I'll edit the original post now.

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    Take off 69 (or what ever idler is) and replace with 37/47 compound idler

    Put QC box in the 20 TPI position

    Cut 1mm thread, but do not disengage half nuts (you have to reverse spindle - or turn it backwards by hand)

    How this works:

    37/47 compound is very close to being a 1.27 to 1 compound

    20 TPI is .050" lead

    .050 divided by 1.27 is ,03937, which is 1mm

    Likely need ALSO some tooth count idler just to reach the 64 tooth

    Maybe your quadrant will accommodate this, maybe not

    (1.2777 compound will be off about .012" at the 2" length)

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    Quote Originally Posted by johnoder View Post
    Take off 69 (or what ever idler is) and replace with 37/47 compound idler

    Put QC box in the 20 TPI position

    Cut 1mm thread, but do not disengage half nuts (you have to reverse spindle - or turn it backwards by hand)

    How this works:

    37/47 compound is very close to being a 1.27 to 1 compound

    20 TPI is .050" lead

    .050 divided by 1.27 is ,03937, which is 1mm

    Likely need ALSO some tooth count idler just to reach the 64 tooth

    Maybe your quadrant will accommodate this, maybe not

    (1.2777 compound will be off about .012" at the 2" length)
    Hi John, Thanks for the info.

    I have seen that solution online but I prefer the option of using the a 63T compounded with existing 80T idler. That ratio is closer to 1.27 and it should fit using the existing banjo and without the need of a extra idler.

    I've just had a quote of $25 to make a a 63T , DP14, PA 14.5 spur in Delrin. It's not going to be an issue in terms of durability as it'll be used very rarely.

    I'm no machinist so please, anyone, let me know if you see a potential flaw in this plan

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    plan is fine as long as you can fix it to the 80T gear securely.

    BTW- thread dial is useless for metric threads.

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    Quote Originally Posted by iwananew10K View Post
    plan is fine as long as you can fix it to the 80T gear securely.

    BTW- thread dial is useless for metric threads.
    Thanks. There's a decent boss on the existing 80T idler that I can machine down to an 1"1/4, I can then drill and tap a few fixings thro the delrin gear into the 80T. I'll add spacers to align the drive with the 64T gearbox drive gear. Re- the thread dial, yes , I also thought it would be completely out of sync so I'll follow Johns advice and keep the half nut engaged.

    I'll post a few pics when it's sorted.

    Thanks
    Roy

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    Actually CLOSER than the 37/47 - plus a maybe more handy size as far as reaching to 64 tooth


    Quote Originally Posted by Westie View Post
    Hi John, Thanks for the info.

    I have seen that solution online but I prefer the option of using the a 63T compounded with existing 80T idler. That ratio is closer to 1.27 and it should fit using the existing banjo and without the need of a extra idler.

    I've just had a quote of $25 to make a a 63T , DP14, PA 14.5 spur in Delrin. It's not going to be an issue in terms of durability as it'll be used very rarely.

    I'm no machinist so please, anyone, let me know if you see a potential flaw in this plan

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    Quote Originally Posted by johnoder View Post
    Actually CLOSER than the 37/47 - plus a maybe more handy size as far as reaching to 64 tooth
    Jobs a good'un, cutting perfect 1mm threads with the QCGB set on B3 (20TPI). The back gear cover now needs to be lifted slightly to clear the 64T gear driving the QCGB as it now has a 5/8" spacer behind it.

    Thanks for help and advice.

    img_20190710_193755.jpgimg_20190710_193728.jpgimg_20190710_193648.jpg

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    Wonderful photos of a compound gear train - thank you

    Again - the not very complicated math
    80 divided by 63 = 1.26984 to 1 - VERY close to 1.27 to 1

    20 TPI has a lead of .050"

    .050 divided by 1.26984 = .039375" which is VERY close to 1 mm

    Westie could put it in 40 TPI and cut 1/2mm

    or 10 TPI and cut 2 mm

    or 5 TPI and cut 4 mm

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    Quote Originally Posted by johnoder View Post
    Wonderful photos of a compound gear train - thank you

    Again - the not very complicated math
    80 divided by 63 = 1.26984 to 1 - VERY close to 1.27 to 1

    20 TPI has a lead of .050"

    .050 divided by 1.26984 = .039375" which is VERY close to 1 mm

    Westie could put it in 40 TPI and cut 1/2mm

    or 10 TPI and cut 2 mm

    or 5 TPI and cut 4 mm

    Yes, basically I can just take TPI off the QCGB chart, multply by 1.26984/25.4 for the metric thread pitch equivalent (if one exists).

    Threading with the half nut permanently engaged is a bit of a PITA I have to say, I've put a Chinese inverter on now (something I've been meaning to do for ages) as it brakes the motor to a quick stop, reducing the run on. Is there any way to modify the thread dial to get it back in sync?

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    Quote Originally Posted by Westie View Post
    Yes, basically I can just take TPI off the QCGB chart, multply by 1.26984/25.4 for the metric thread pitch equivalent (if one exists).

    Threading with the half nut permanently engaged is a bit of a PITA I have to say, I've put a Chinese inverter on now (something I've been meaning to do for ages) as it brakes the motor to a quick stop, reducing the run on. Is there any way to modify the thread dial to get it back in sync?

    You don't have to leave the half-nuts engaged, just ensure that they always return to the exact same position. This might sound like a hard thing to do, but it's really not that tough. Here's a video. I've been doing all my metrics like this:


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    Quote Originally Posted by GenePoole View Post
    You don't have to leave the half-nuts engaged, just ensure that they always return to the exact same position. This might sound like a hard thing to do, but it's really not that tough. Here's a video. I've been doing all my metrics like this:

    Thanks for that excellent video! It's a much easier way, especially now stopping and reversing with a VFD is so smooth and easy.

    Just wondered if you had ever tried cutting a thread like that by mounting the tool upside down on the back side of the work with the spindle in reverse, so you can cut a RH thread feeding away from the chuck, it's easier on my heart and safer if I'm feeling dozey

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    Just wondered if you had ever tried cutting a thread like that by mounting the tool upside down on the back side of the work with the spindle in reverse,
    Worked great on Monarch. Similar concept is applicable to use of taper attach settings for both OD and ID
    Attached Thumbnails Attached Thumbnails p1000383sm.jpg  

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    Quote Originally Posted by Westie View Post
    Thanks for that excellent video! It's a much easier way, especially now stopping and reversing with a VFD is so smooth and easy.

    Just wondered if you had ever tried cutting a thread like that by mounting the tool upside down on the back side of the work with the spindle in reverse, so you can cut a RH thread feeding away from the chuck, it's easier on my heart and safer if I'm feeling dozey
    I've never tried threading upside down, but I believe you need a relief cut for that and I'm not sure how you'd do your forward/reverse synchronization. I've never used a relief cut; my mentor wouldn't let me. I made hundreds of threads on scrap before ever trying it on a real workpiece. I crashed into the shoulder dozens of times and broke and recut dozens of HSS tools. In retrospect, I think that was probably the best method to get good at threading.

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    Quote Originally Posted by johnoder View Post
    Wonderful photos of a compound gear train - thank you

    Again - the not very complicated math
    80 divided by 63 = 1.26984 to 1 - VERY close to 1.27 to 1

    20 TPI has a lead of .050"

    .050 divided by 1.26984 = .039375" which is VERY close to 1 mm

    Westie could put it in 40 TPI and cut 1/2mm

    or 10 TPI and cut 2 mm

    or 5 TPI and cut 4 mm
    Hmmm... any ideas on cutting a 1.5mm thread pitch?

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    Quote Originally Posted by Westie View Post
    Hmmm... any ideas on cutting a 1.5mm thread pitch?
    He's using the 64 tooth as the final gear in the train. There should be a 48 tooth gear included with most SB13s. It is used as a stud gear for the very coarse thread pitches (4, 4.5, 5, 5.5, 5.75, 6, 6.5, 7). I've used the 48T before in place of the 64T to cut 27 TPI threads (1). The ratio is 48/64 or 3/4 so 36TPI *3/4 = 27 TPI. Using the same math, a 2.0mm thread would become a 1.5 thread with the 48T gear in place of the 64T gear: 2.0 * 3/4 = 1.5.


    1: 27 TPI on SB13?
    Last edited by GenePoole; 07-15-2019 at 09:29 AM. Reason: Added link

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    As a more than 1 way to skin the kittie, since the OP already has the translation in place (80/63) couldnt the 48T also go on the stud position to generate the 1.5?

    And if a 40T gear can be sourced the 1.25mm pitch would also be covered too?

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    So - switch to 10 TPI and 48T final - see is it doos .05906" per turn

    .100" divided by 1.26984 = .07875"

    .07875 times .75 = .05906"

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    Quote Originally Posted by GenePoole View Post
    He's using the 64 tooth as the final gear in the train. There should be a 48 tooth gear included with most SB13s. It is used as a stud gear for the very coarse thread pitches (4, 4.5, 5, 5.5, 5.75, 6, 6.5, 7). I've used the 48T before in place of the 64T to cut 27 TPI threads (1). The ratio is 48/64 or 3/4 so 36TPI *3/4 = 27 TPI. Using the same math, a 2.0mm thread would become a 1.5 thread with the 48T gear in place of the 64T gear: 2.0 * 3/4 = 1.5.


    1: 27 TPI on SB13?

    Wow! Thankyou. That's quite a feat of lateral thinking, and I do have the 48T stud gear. I can also use that solution for a 3mm thread.

    I've only just started to realise what an iconic machine I've been using for the last 20 years! The history of the Southbend Lathe Co, is fascinating.

    I just realised that the SN I posted in the OP must be an old owner asset number, the actual SN is 8335TKL14, looking at the database I guess it's about 1961. The lathe still has the wholesalers name plate on it 'Buck&Hickman', they're still going, founded 1830!


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