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  1. #1
    Join Date
    Nov 2018
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    Slightly left of Vernon, BC Canada
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    67

    Default 260 end gears need some help with what goes where, what is factory original?

    Hi folks,

    I am working my way thru both of my 260's, one is the AT the other ATLH. They both came from the same high school, one is 18709, the other is 19995.

    To start I am trying to figure out what end gears were factory original for these machines, stud and screw gears, idler always seems to be 80T. The regular machine has 20/30 stud gear and 40/56 screw gears, the ATLH has 20/30 stud and 40/45 screw gears, both 80T idler. I have found multiple threads about similar topics but couldn't really find what is original and is required so that the lead screw turns correctly as indicated on the gear box feed chart. I looked in the parts manual but it is quite confusing as it doesn't explain what was original, it just states what lathes the gears could have been used on.

    I am teaching my son about threading and would like to know the threads we cut are correct.

    And....he also likes Japanese cars and has 2 to maintain, so we will need to cut metric as well. I know we are missing the 60/63 gear as well as all of the others needed to cut metric on an imperial lead screw...I'll tackle this metric thing after we get the imperial sorted.

    As an aside, is there an actual "instruction manual" for the 260 that I am unaware of? I have the maintenance manual, parts manual and TBOT, which I will re-read, but the TBOT doesn't state you need gear X to go here and gear Y to go here for metric or imperial. I also have looked at the gear charts which came on various models, and it is a bit confusing ( for me anyway)

    Here are the 2 gear trains I have, it works and seems okay but it doesn't look like the pictures in the manuals, ie missing a gear.

    Cheers and thanks for all the help.
    Attached Images Attached Images

  2. #2
    Join Date
    Oct 2004
    Location
    Southern Highlands NSW
    Posts
    1,381

    Default

    My 260A is a metric version, but I have this info on imperials for standard gear train: 20, 40, 45.
    There's probably a big idler gear in there somewhere too (number of teeth not important).
    I can't remember where the info came from, possibly from another Hercus owner.

    Here's the transposing gear arrangement for an imperial leadscrew 260.
    Attached Images Attached Images

  3. #3
    Join Date
    Nov 2007
    Location
    melbourne australia
    Posts
    2,307

    Default

    Quote Originally Posted by Kilohertz View Post
    As an aside, is there an actual "instruction manual" for the 260 that I am unaware of? I have the maintenance manual, parts manual and TBOT, which I will re-read, but the TBOT doesn't state you need gear X to go here and gear Y to go here for metric or imperial.
    The TBOT is the instruction manual. Do you have the old pre-metric version of the TBOT or the later version?
    I have a hard copy of the later version so I can photograph and send you the appropriate pages if you want.
    Chris

  4. #4
    Join Date
    Nov 2018
    Location
    Slightly left of Vernon, BC Canada
    Posts
    67

    Default

    Hi Jordan, Chris,

    Well shxt house mouse, I didn't know there was another version of the TBOT. I have been referring to the one I downloaded so I could keep my pristine copy that came with the lathes in it's little ziploc bag...Jeeez, that hardcopy is 1989, my downloaded copy is 1970.... So I will wash my hands, put on my best white gloves and open it for a read, I anticipate the puzzle could be solved if all the gear info is in there. Thank you!

    And that is a great gear chart, same as the one on the end of my lathe, except I can READ yours. So it looks like I am missing a gear, even for imperial. I tried spinning the chuck tonight with the gear box in 8 TPI, and I get 2 revs of chuck to 1 of lead screw, which means ( I think) that I have the 20 tooth stud gear. Now, I need some clarification on the stud gear, mine has 20 teeth on the outside, driving the 80T idler, the tumblers are driving a 30T gear which is part of the 20T casting, so it's a 20/30T all cast into one. There must be a 40/30T gear?? which is what is missing from my machines, which goes on the stud below the tumblers, correct?

    I am going to call the high school again to see if they could locate this, after I hear back from you fine gents.

    Meanwhile, I'll try to get to reading the newly found version of my TBOT to see if anything new helps me.

    Thanks boys!

    Cheers!

  5. #5
    Join Date
    Jan 2009
    Location
    Holbrook, NSW
    Age
    69
    Posts
    382

    Default imperial 260 standard gears

    Quote Originally Posted by Kilohertz View Post
    Hi folks,

    I am working my way thru both of my 260's, one is the AT the other ATLH. They both came from the same high school, one is 18709, the other is 19995.

    To start I am trying to figure out what end gears were factory original for these machines, stud and screw gears, idler always seems to be 80T. The regular machine has 20/30 stud gear and 40/56 screw gears, the ATLH has 20/30 stud and 40/45 screw gears, both 80T idler. I have found multiple threads about similar topics but couldn't really find what is original and is required so that the lead screw turns correctly as indicated on the gear box feed chart. I looked in the parts manual but it is quite confusing as it doesn't explain what was original, it just states what lathes the gears could have been used on.

    I am teaching my son about threading and would like to know the threads we cut are correct.

    And....he also likes Japanese cars and has 2 to maintain, so we will need to cut metric as well. I know we are missing the 60/63 gear as well as all of the others needed to cut metric on an imperial lead screw...I'll tackle this metric thing after we get the imperial sorted.

    As an aside, is there an actual "instruction manual" for the 260 that I am unaware of? I have the maintenance manual, parts manual and TBOT, which I will re-read, but the TBOT doesn't state you need gear X to go here and gear Y to go here for metric or imperial. I also have looked at the gear charts which came on various models, and it is a bit confusing ( for me anyway)

    Here are the 2 gear trains I have, it works and seems okay but it doesn't look like the pictures in the manuals, ie missing a gear.

    Cheers and thanks for all the help.
    20 or 40 on the stud gear position, 80 idler and 45 on the gearbox. see attached copy of the gearbox chart. The 20 or 40 sits on the outside of the 45 when not in use.
    Mal
    Attached Images Attached Images

  6. #6
    Join Date
    Oct 2011
    Location
    Norwood-ish, Adelaide
    Age
    54
    Posts
    5,167

    Default

    Quote Originally Posted by Kilohertz View Post
    ...I am teaching my son about threading and would like to know the threads we cut are correct.

    And....he also likes Japanese cars and has 2 to maintain, so we will need to cut metric as well. I know we are missing the 60/63 gear as well as all of the others needed to cut metric on an imperial lead screw...
    Just to rain on the parade a little - the 63t gear is an approximation to metric threading. Over a short distance, the error is slight (0.8%) enough not to matter too much, but to be 'correct' it should be 63 1/2 teeth (or 127 teeth as is normally done). Normally hardly worth pointing out, but as this is a learning exercise

    Michael

  7. #7
    Join Date
    Oct 2009
    Location
    Upwey VIC
    Posts
    166

    Default

    The 63T gear actually allows much more accurate metric/imperial conversion than that:
    Extract from an article by Neil Wyatt:

    The 63 tooth gear arises from another, fortuitous bit of maths.1mm pitch is 25.4 threads per inch. To cut 25.4 tpi on a 16 tpi leadscrew we need a ratio of 16:25.4, this works out at 0.62992:1, or almost exactly 63:100. If we introduce the ratio 63:100 into our gear train then a 16tpi leadscrew will cut a 1mm pitch thread – actually 1.00125mm pitch – well within the tolerance of any other aspect of the process. To translate this into standard change wheels we can use:63/100 = 63/50 *1/2=63/50 x 30/60This means a 63-tooth gear on the fixed stud, driving a 50T joined to a 30T on the intermediate pair, and finally a 60T on the leadscrew itself (photo 2).Conversely, a ratio of 100:63 allows a 1mm metric leadscrew to cut a 16tpi thread with the same accuracy. In fact, the standard metric leadscrew for mini lathes has a pitch of 1.5mm, so the 100:63 ratio would therefore cut 16 x 1.5 = 24 tpi, but this is dealt with by putting the ratios 2/3 and 100:63 in series. To get standard changewheels:100/63 x 2/3 = 50/63 x 4/3 = 50/63 x 4/3 = 50/63 x 40/30Just for clarity, this is a 50-tooth gear on the fixed stud, driving the 63T joined to a 40T on the intermediate pair, and finally a 30T on the leadscrew itself.From these basic ratios, it is possible to derive a ratio for any other metric or imperial thread. Armed with a 63-tooth wheel and the right changewheel ratios you can cut almost any standard metric or imperial thread.

    My C6 lathe uses a 42T gear for the same purpose.

    Andrew


  8. #8
    Join Date
    Mar 2017
    Location
    Sydney
    Posts
    9

    Default

    Kilohertz,

    You might find this helpful. I did when I was trying to teach myself to cut imperial threads with a metric leadscrew.



    I know it's not to do with the necessary gear train sizes but it might just be helpful anyway.

  9. #9
    Join Date
    Oct 2011
    Location
    Norwood-ish, Adelaide
    Age
    54
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    5,167

    Default

    Quote Originally Posted by mahgnia View Post
    The 63T gear actually allows much more accurate metric/imperial conversion than that:
    Extract from an article by Neil Wyatt:

    .... Armed with a 63-tooth wheel and the right changewheel ratios you can cut almost any standard metric or imperial thread.
    My 0.8% is derived from the difference between 63.5 and 63. Neil says it is 0.1% - I can live with that*. However the last statement is incorrect and this is what I was trying to draw attention to - you can not cut a 'standard metric thread' if you don't have a 127t** gear. You can cut an approximation to it, and it will be very close. Over a short distance (say the length of a nut), it will likely not be noticed for fits of threads cut in the home workshop. However, it is there.

    *That is with a 16tpi leadscrew. The Hercus machines are 8tpi from memory. There is now a factor of 2 to include to get up to that nearly whole number

    **127 is the first integer number that you get from multiplying 25.4 with an integer number if inches (5)***

    ***Been reading Terry Pratchett again

    Michael

  10. #10
    Join Date
    Nov 2007
    Location
    melbourne australia
    Posts
    2,307

    Default

    My head is starting to hurt.

    Quote Originally Posted by Kilohertz View Post
    They both came from the same high school, one is 18709, the other is 19995.
    That makes both machines mid- to late-80s vintage. Are you saying one or both of them is an imperial machine?
    Chris

  11. #11
    Join Date
    Jan 2009
    Location
    Holbrook, NSW
    Age
    69
    Posts
    382

    Default 60/63 and 63/64

    Just for the record, the 60/63(for imperial to metric conversion) and the 63/64 (for metric to imperial conversion) was adopted by Hercus with their 260 lathes and became a stock item in their 260 spare parts books, which didn't even list the larger gears at all. It seems very unlikely they would have been done this, if the error was significant. In my investigations of this, I found a small error in the 4th decimal place of the final output ratio of the gearbox, which translated into a virtually immeasurable error in the thread, which in all practical terms was pointless to chase.
    The size and weight and price of the 100/127 and 120/127 gears, in my opinion, doesn't justify their use. While I keep a stock of the larger gears for the traditionalist, most sales are for the smaller ones. The attached pics show the original conversion plates supplied as stock items from Hercus, for their imperial models of 9" and 260.
    Mal
    Attached Images Attached Images

  12. #12
    Join Date
    Nov 2018
    Location
    Slightly left of Vernon, BC Canada
    Posts
    67

    Default

    Quote Originally Posted by jack620 View Post
    That makes both machines mid- to late-80s vintage. Are you saying one or both of them is an imperial machine?
    Early one is 1987 I think and the later one is 1990. Have the inspection slip for the later one and Mal dated the earlier on in one of my very early posts on this forum.

    And yes, both imperial machines.

    Cheers

  13. #13
    Join Date
    Nov 2018
    Location
    Slightly left of Vernon, BC Canada
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    Thanks Mal,

    This is the plate that is on my ATLH machine 18706. The later AT machine has no tag 19995.

    Thanks



    260 end gears need some help with what goes where, what is factory original?-5h597-inch-metric-260at-jpg

  14. #14
    Join Date
    Nov 2018
    Location
    Slightly left of Vernon, BC Canada
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    Default

    THANKS everyone for all of the information, really appreciated. I finally have a day off this weekend and will be playing in the shop all day tomorrow. I am going to pull all the end gears off both machines and figure out what I have and how they work with each other. With all the replies here, I think I now have a better understanding of how the gears work, and I was mistaken thinking the 20/30 gear the tumblers drive was a compound gear, I believe now that they are 2 gears, maybe a keyed shaft and the 40T that is on the outside of the 45T screw gear is actually my 40T stud gear.

    Now I realize I need more gears to thread metric, will SB gears work on Hercus machines? Me being in north america, they will be easier/cheaper to find locally. If not, I know Mal has them.

    Anyway, thanks again.

    Weekend here we come!

    Cheers

  15. #15
    Join Date
    Oct 2004
    Location
    Southern Highlands NSW
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    Default

    Quote Originally Posted by Kilohertz View Post
    will SB gears work on Hercus machines?
    Yes

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