Results 1 to 5 of 5

Thread: Metric Threads on a Lathe

  1. #1
    Indian Admin Winn R's Avatar
    Join Date
    Feb 2004
    Location
    About 40 mi. north of Atlanta.
    Posts
    5,930
    Feedback Score
    18 (100%)

    Default Metric Threads on a Lathe




    For those of you with old change gear lathes such as South Bend or Logan, metric threads can be a challenge. The numerically correct gears are 127 and 100 and are ridiculously expensive.


    It is possible to take your collection of gears and break each in to its factors and try to work out ratios closest to the ratio of the lead screw thread and 25.4. It's doable but a real PITA.


    Here's a program which, although not very user friendly, actually works. Download it, unzip it, open the text file and insert the metric lead screw thread (generally 8tpi), drive gear, then list every gear you have.


    It will give you the best gear ratios for any given metric thread and the error from the mathematically correct thread.

    http://titaniumstudios.com/tooljunki...angegears.html


    There is no nonsense so errant that it cannot be made the creed of the vast majority by adequate governmental action. -- Bertrand Russell


    "Never attribute to malice that which can be adequately explained by stupidity." Robert J. Hanlon

  2. #2
    GuncoHolic yosuthnmasa's Avatar
    Join Date
    Mar 2004
    Location
    SW, GA
    Posts
    2,067
    Feedback Score
    4 (100%)

    Default

    Quote Originally Posted by Winn R


    For those of you with old change gear lathes such as South Bend or Logan, metric threads can be a challenge. The numerically correct gears are 127 and 100 and are ridiculously expensive.


    It is possible to take your collection of gears and break each in to its factors and try to work out ratios closest to the ratio of the lead screw thread and 25.4. It's doable but a real PITA.


    Here's a program which, although not very user friendly, actually works. Download it, unzip it, open the text file and insert the metric lead screw thread (generally 8tpi), drive gear, then list every gear you have.


    It will give you the best gear ratios for any given metric thread and the error from the mathematically correct thread.

    http://titaniumstudios.com/tooljunki...angegears.html


    What use a program? I bet you learned how to do this by hand back in the day! In fact, they're still teaching us how to do gear ratios/reductions, etc. in school. How close did you get the threads with the gears you have?

    Josh
    member 143

  3. #3
    Indian Admin Winn R's Avatar
    Join Date
    Feb 2004
    Location
    About 40 mi. north of Atlanta.
    Posts
    5,930
    Feedback Score
    18 (100%)

    Default

    Josh -- running them by hand was what made me hunt up the program!!

    This is one of the more accurate combinations.


    # This first number is the pitch of the lead screw (in metric).
    # 3.175 is 8 TPI.

    3.175

    # This second number is the number of teeth on the drive gear.

    24

    # The rest of the numbers are gear sizes (defined by number of teeth) that I have.

    16
    18
    24
    24
    32
    32
    36
    40
    44
    46
    48
    52
    54
    56
    56
    60
    64
    64
    72
    80




    THREAD STUD1 STUD2 LEAD ERROR
    6.00 5.95 IDLER 16/60 48 0.007813
    5.50 5.50 IDLER 18/52 40 0.000606
    5.00 5.00 IDLER 18/52 44 0.000606
    4.50 4.52 IDLER 18/64 60 0.003457
    4.00 4.02 IDLER 16/54 64 0.004590
    3.50 3.49 IDLER 40/44 24 0.002143
    3.00 3.01 IDLER 44/80 46 0.003953
    2.75 2.75 IDLER 18/52 80 0.000606
    2.50 2.50 IDLER 36/52 44 0.000606
    2.25 2.25 IDLER 40/52 44 0.000606
    2.00 2.00 IDLER 44/60 52 0.000874
    1.75 1.75 IDLER 56/72 56 0.000292
    1.50 1.50 IDLER 44/52 60 0.000606
    1.25 1.25 64/54 72/56 40 0.000125

    1.00 1.00 60/54 80/56 48 0.000125 --- running 14-1 lh on barrel ends, I can't tell the difference between this and perfect threads.

    0.90 0.90 46/40 60/44 54 0.000179
    0.80 0.80 44/36 64/46 56 0.000241
    0.75 0.75 60/54 80/56 64 0.000125
    0.70 0.70 44/36 64/46 64 0.000241
    0.60 0.60 46/32 72/44 54 0.000179
    0.50 0.50 64/56 60/36 80 0.000125
    0.01 0.06 64/16 72/18 80 4.953125
    Last edited by Winn R; 09-20-2007 at 07:46 PM.
    There is no nonsense so errant that it cannot be made the creed of the vast majority by adequate governmental action. -- Bertrand Russell


    "Never attribute to malice that which can be adequately explained by stupidity." Robert J. Hanlon

  4. #4
    Plinker762's Avatar
    Join Date
    Feb 2004
    Location
    Spokane
    Posts
    229
    Feedback Score
    20 (100%)

    Default

    Also, when cutting metric threads with an inch lead screw, you can't use the threading dial. You have to leave the half nut engaged and reverse the spindle to back up on the cut.

  5. #5
    Indian Admin Winn R's Avatar
    Join Date
    Feb 2004
    Location
    About 40 mi. north of Atlanta.
    Posts
    5,930
    Feedback Score
    18 (100%)

    Default

    Hey Frank -- yes, never disengage.

    I'm the poster boy for incompetence in self taught OJT. At first I didn't figure the effect of backlash when the bit reversed --I started only backing it out 3 or 4 thousandths and wondered why the threads were tall and skinny!!

    I have to cut a groove to start. Have you seen the perfect start of the factory ones? Maybe they use a die but it looks like only a single pass.
    There is no nonsense so errant that it cannot be made the creed of the vast majority by adequate governmental action. -- Bertrand Russell


    "Never attribute to malice that which can be adequately explained by stupidity." Robert J. Hanlon

Search tags for this page

There are currently no search engine referrals.
Click on a term to search our site for related topics.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •