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Thread: Cutting Metric threads on a American Lathe

  1. #11
    Join Date
    Aug 2006
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    Beaverton, OR
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    7,332

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    Quote Originally Posted by Mcgyver
    The reason why the 127 works is 5 x 25.40000000000000 = 127.0000000000000 and the international inch is defined at being exactly 25.4mm.
    Unless you are on a Pentium, than it is 127.000000000001

  2. #12
    Join Date
    Aug 2004
    Location
    Barrie ontario Canada
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    193

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    Hi Guys
    Well I have been doing a ton of reading since posting this topic. I am far from getting a handle on this metric threading. Im still lost on alot of this stuff but doing my best to learn.

    I did get a copy of the manual for my lathe from a PM member that has the same machine. In the manual, there is alot of infro on the end gears for metric threading, so what Im try to do, isnt impossible, but very confusing to me.

    The manual shows the gear train set up for what they call STD End Gearing.
    There is one thing that stumps me with this, the idler gear is claimed to be 72 tooth, and mine is 60.
    Hoping I have this right, the gears are as follows
    Top , Stud gear 32 tooth
    2nd, idler gear 60 tooth
    3rd tumbler gear 36 tooth
    4th gear box 48 tooth
    The manual says these are 12P, and 20 o PA is stamped on the face of the gears
    Question: does the idler gear tooth not count part of all the ratio,s?
    Im supposed to have a 72T and I have a 60 T
    I have cut many different TPI threads on this lathe, and for anything I have done, its allways worked out fine.

    The drawing for metric end gearing shows the 127T comp gear with the 60T behind it. Also has a chart for stud gears ranging from 32 to 56 . It also shows the idler as a 40t gear. So I get the feeling Im going to need a 127-T, and a 40-T and a few different tooth counts for the stud gear to get common pitches in millimeters.

    Is there any threading guru,s here that would look at these charts, and try to make some sense out of all this for me?

    One of the posters had mentioned about having a threading dial, leadscreww to reverse, that would be yes on both counts, the lathe is equipped with both. The the lathe is 5hp 3 phase so the carriage can be reversed one way or the other with the half nuts closed.

    A few questions before I go.
    The manual says the gears are 12-P , is that the dia pitch?
    and on the face of the end gears is stamped 20o PA , is this the pressure angle? Reason Im asking is , if I was to order a gear,or gears. I would think tooth count, pitch & pressure angle would be the information they would need to know.
    Im hoping to learn enough about this before my hair gets any grayer, or I rip it all out in the process,lol.

    Thanks for the input guys
    Paul

  3. #13
    Join Date
    Sep 2003
    Location
    Louisville, KY
    Posts
    798

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    Idler gears don't count in the gear ratios.
    Apparently you have 12 diametrical pitch and 20* pressure angle gears.
    Harry

  4. #14
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    Feb 2009
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    LaPorte County, Northwest Indiana
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    This should become a sticky.

  5. #15
    Join Date
    Oct 2004
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    Prestatyn, North-Wales
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    The drawing for metric end gearing shows the 127T comp gear with the 60T behind it. Also has a chart for stud gears ranging from 32 to 56 . It also shows the idler as a 40t gear. So I get the feeling Im going to need a 127-T, and a 40-T and a few different tooth counts for the stud gear to get common pitches in millimeters
    You don't need as many as you think ..a lot of them double for double mms pitch..so a 1mm pitch set up will also do a 2mm and 4mm pitch, if i remember right ..so on and on ..you just change the stud gear and use the chart for the gearbox settings.
    the full set that is recommended ..covers some obscure pitches that you will never use in a life time. like 0.9 pitch

    here's the metric chart for a 9 inch south bend with screw cutting gearbox

    if you haven't got the screw cutting gearbox ..then good luck to you ..i don't think i would bother.



    here's the gear set for South bend 9 to cut all "common" metric threads if lathe has screw cutting gearbox.



    all the best.markj

  6. #16
    Join Date
    May 2003
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    52N 122W Western Kanuckistan
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    40,423

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    Here are my instructions on how to use the existing change gears for a South Bend 9C to cut most metric threads with an error of only 2 threads per metre. No special gears are required.

    http://ixian.ca/gallery/metric/metric.htm
    Free software for calculating bolt circles and similar: Origin now settable to bottom left! All values positive. Click Here

  7. #17
    PeteF Guest

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    Quote Originally Posted by aboard_epsilon
    if you haven't got the screw cutting gearbox ..then good luck to you ..i don't think i would bother.
    I'm interested in why you say that, as I was just about to order a set of transposing gears for my imperial C model. I've never cut metric threads on this lathe, I thought it would be no more hassle than the usual imperial gear juggling act. These are the ones I was looking at BTW http://cgi.ebay.com.au/NEW-METRIC-TR...#ht_2575wt_907

  8. #18
    Join Date
    Jun 2004
    Location
    Anniston, AL
    Posts
    1,099

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    Quote Originally Posted by 8ntsane
    The manual shows the gear train set up for what they call STD End Gearing.
    There is one thing that stumps me with this, the idler gear is claimed to be 72 tooth, and mine is 60.
    Hoping I have this right, the gears are as follows
    Top , Stud gear 32 tooth
    2nd, idler gear 60 tooth
    3rd tumbler gear 36 tooth
    4th gear box 48 tooth
    The manual says these are 12P, and 20 o PA is stamped on the face of the gears
    Question: does the idler gear tooth not count part of all the ratio,s?
    Im supposed to have a 72T and I have a 60 T
    I have cut many different TPI threads on this lathe, and for anything I have done, its allways worked out fine.

    The drawing for metric end gearing shows the 127T comp gear with the 60T behind it. Also has a chart for stud gears ranging from 32 to 56 . It also shows the idler as a 40t gear. So I get the feeling Im going to need a 127-T, and a 40-T and a few different tooth counts for the stud gear to get common pitches in millimeters.
    I think you have it figured out correctly. The 127T and the 60T form the compound gear to get your basic metric conversion. The listed stud gears and corresponding gearbox setting give you the different MM pitches. If you only want to cut certain pitches then you will need the stud gears only for those pitches. Most systems give a pretty extensive range with five or six stud gears.

    There are many, many, different gear setups for doing this but you are unlikely to find another method better than the one the lathe manufacturer has worked out and recommends unless you only want a more limited range of pitches.
    Don Young

  9. #19
    Join Date
    Jun 2004
    Location
    Anniston, AL
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    1,099

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    Quote Originally Posted by PeteF
    I'm interested in why you say that, as I was just about to order a set of transposing gears for my imperial C model. I've never cut metric threads on this lathe, I thought it would be no more hassle than the usual imperial gear juggling act. These are the ones I was looking at BTW http://cgi.ebay.com.au/NEW-METRIC-TR...#ht_2575wt_907
    The only problem with cutting metric threads without a gearbox is that it takes a more gears. If you already have the full English set then the number of additional gears is about the same. The English gearbox has a pretty limited number of ranges useful for metric threading. That gear set is the same as the one originally furnished by South Bend and will cut all of the pitches listed on the chart. That is a very good selection of pitches. It is no more difficult to change the pitch for metric threading than for English, but you have the additional need for changing between the two systems, whether you have a gearbox or not.
    Last edited by Don Young; 04-06-2011 at 10:49 PM.
    Don Young

  10. #20
    Join Date
    Sep 2003
    Location
    Louisville, KY
    Posts
    798

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    A 127T 12DP gear is 10.75" OD. Make sure that you can get that gear in the space. The reason that Monarch changes the DP on the metric conversion gears is that they couldn't get their standard pitch gears in the space.
    A couple of other factors to consider are; the face width of the purchased vs the original gears and the load rating, and the availibility of the gears from stock, you just may get into the gear cutting business.
    Harry

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