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  1. #1
    Join Date
    Jan 2017
    Location
    Toronto NSW
    Age
    73
    Posts
    8

    Default Model C Gearing for Metric Screwcutting

    I am a self-taught novice on my late father's Model C. I am looking to turn a 1.25mm pitch thread for a carburetor jet in a veteran car. Two questions:

    1. the chart on the lathe gear cover specifies a 27 stud gear but the Hercus book (p61 of the 1980 ed) specifies a stud gear of 24. Which is correct? To confuse matters further the book specifies a gear number for 1.0mm pitch which has been crossed out and 27 has been handwritten there (by my father I assume).

    2. a 63/60 compound gear is specified - does the 63 run closest to the lathe or the 60? I'm finding it a bit hard to work out the diagrams!

    Jeff

  2. #2
    Join Date
    Jun 2007
    Location
    sydney ( st marys )
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    64
    Posts
    4,887

    Default

    Is the lathe a 9" or 260?

  3. #3
    Join Date
    Apr 2016
    Location
    New South Wales
    Posts
    45

    Default

    Hercus_TextBook_of_Turning-31.jpg

    Viewers should be able to download that image (after logging in) and then zoom in on it for the details.

    This is probably a different (earlier) edition of the Hercus Textbook of Turning, with instructions suitable for 9" Model B & C, and it relies on using the 127/100 transposing gear.

    In FIG 3., on the screw pitch thread chart on the right, (of Figure 139, i.e. "FIG. 3 on Figure 139", getting a little complicated) the marking of the 18T side of the 72/18 compound gear is omitted (design error, or perhaps they did not copy the South Bend chart they are cloning this from fully/correctly). Although there is present the unidentified arrow pointing at the (obscured) 18T gear (obscured behind the 72).

    It appears to me that on this set of diagrams the 127 tooth gear of the transposing pair 127/100 is mounted closest to the headstock. (But I am not sure whether my interpretation of the diagram is correct, nor am I sure if the diagram is correct.)

    For 1.25 mm threads, according to the chart, and diagram - FIG 2. in particular - the 127T side of the transposing gear drives the 40T stud gear and the 80T screw gear drives the 100T side of the transposing gear.

  4. #4
    Join Date
    Nov 2010
    Location
    Gippsland Victoria
    Posts
    733

    Default metric threads

    There are various books and web sites that explain how to do the relevant calculation that gives the you the final TPI for any given gear train. If you google "metric thread imperial lathe 8tpi leadscrew calculator" you will find various discussions and calculators

    Here is a page I found useful Metric Threading

    Best thing I found was a free program written by a chap on this forum called Vernon, the program was called lathegears and you give it a list of all of your gears and then the tpi of your leadscrew and it it will calculate what gear trains will cut the the required thread - you can set a tolerance on the required thread ie +/- x.x% -its a very very good calculator. Link below ...

    Lathe thread cutting change gear calculator [Archive] - Woodwork Forums

    Bill

  5. #5
    Join Date
    May 2011
    Location
    Murray Bridge S Aust.
    Age
    71
    Posts
    5,942

    Default

    Bill, unfortunately the link comes up with an "Invalid Attachment specified. If you followed a valid link, please notify the administrator"
    Kryn
    To grow old is mandatory, growing up is optional.

  6. #6
    Join Date
    Apr 2016
    Location
    New South Wales
    Posts
    45

    Default

    Quote Originally Posted by KBs PensNmore View Post
    Bill, unfortunately the link comes up with an "Invalid Attachment specified. If you followed a valid link, please notify the administrator"
    Kryn
    Both links worked for me (when I tried them about 10 minutes later than KBs PensNmore tried them)

  7. #7
    Join Date
    May 2011
    Location
    Murray Bridge S Aust.
    Age
    71
    Posts
    5,942

    Default

    Just tried it again, it comes up with this page; Lathe thread cutting change gear calculator
    Lathe thread cutting change gear calculator

    I then click on "Here is the link http://www.woodworkforums.com/attach...1&d=1275121329"
    Woodwork Forums
    and I get "Invalid Attachment specified. If you followed a valid link, please notify the administrator"

    So what am I doing wrong??
    Thanks
    Kryn
    To grow old is mandatory, growing up is optional.

  8. #8
    Join Date
    Nov 2010
    Location
    Gippsland Victoria
    Posts
    733

    Default

    Kryn,

    More than one way to skin this cat ......Try this

    Google "lathe thread cutting change gear calculator metalworkforums.com"

    should be the first thing that google finds.

    Problems might be due to archived tapatalk part of forums ... ? I dont know.

    Bill

  9. #9
    Join Date
    May 2011
    Location
    Murray Bridge S Aust.
    Age
    71
    Posts
    5,942

    Default

    Thanks Bill, I still get the same message??
    To grow old is mandatory, growing up is optional.

  10. #10
    Join Date
    Nov 2010
    Location
    Gippsland Victoria
    Posts
    733

    Default

    Quote Originally Posted by KBs PensNmore View Post
    Thanks Bill, I still get the same message??
    Kryn,

    Something to do with the archived forums ? Maybe raise it with the forum admin people ?

    Have sent you a PM

    Bill

  11. #11
    Join Date
    Apr 2016
    Location
    New South Wales
    Posts
    45

    Default

    Whoops, now I am infected.

    Lathe thread cutting change gears.jpg

    Or more correctly I was infected all along ? The bird landing on its head corresponds to the file not being at the given location. "To be or not to be ?"

  12. #12
    Join Date
    Nov 2010
    Location
    Gippsland Victoria
    Posts
    733

    Default Try this

    OK original download links seem broken.

    See attached zip file and output example called output.pdf

    I don't think I am breaking any copyrights by putting this up - see attached jpg file called about.jpg where permission is given to distribute the program.

    I've tried this zip file on a laptop and it works - don't extract the files into the official windows programs folder because if you do that you wont get permission to input your own change wheels.

    Its a terrific program and the chap deserves lotsa applause for writing it.

    Bill
    Attached Images Attached Images
    Attached Files Attached Files

  13. #13
    Join Date
    May 2011
    Location
    Murray Bridge S Aust.
    Age
    71
    Posts
    5,942

    Default

    Thanks Bill, Managed to down load it.
    Kryn
    To grow old is mandatory, growing up is optional.

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