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  1. #1
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    Dec 2008
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    Default Metric versus Imperial Lathes

    Some basic but relevant questions for people new to the accuracy of metal lathes.
    Given the degree of measuring of actual components does it matter if you have an imperial or metric lathe for turning?
    Will Imperial lathes cut metric threads and vice versa without changing the lead screw?
    Can these be done with a change in just the back gears?
    What needs changing on a 260 with a gearbox to achieve both ?
    Given the choice which one would you choose?
    Cheers from Micheal.
    Last edited by localele; 13th Jan 2012 at 07:34 AM. Reason: More thoughts

  2. #2
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    Dosent matter if lathe is Metric or Imperial.

    No need to change leadscrew to cut Metric or Imperial.

    Metric or Imperial threads just require a change of the Change gears and the correct selection of the levers on the gearbox to achieve the threads.

    On the 260 AM you can cut metric threads by just changing the 45 tooth gear with the 18 tooth gear as shown on the Threading/Feeding plate on the quick change gearbox.

    To cut Imperial threads on a 260 AM you would require the following change gears and compound gear 25,33,39,42,48 and 50 tooth chage gears and a 63/64 compound.

    If you knew before hand that you would be cutting mainly Metric threads I would select a Metric lathe and vice a versa.

    There would be no need to purchase or acquire all the change gears if only a select amount of Imperial threads were to be cut.

    If you had an 260 A and wished to cut Metric threads you would require the following change gears and compound 20,24,25,30,33,40,42,50 ,80 tooth idler and a 60/63 compound gear.

    Choice dosent really matter as all things can be worked around,if Imperial threads were the main thread form being cut you would likely go for the 260 A.

    Unfortunately there appears to be many more 260AM or 260C/BM lathes available than the 260A or 260C/B.

  3. #3
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    Micheal,

    For a bit of light reading on the subject of screwcutting, have a look at this earlier thread. I have a pair of nines, both A's. I wish one was metric.

    http://www.woodworkforums.com/f189/c...hreads-141692/

    BT

  4. #4
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    Thanks Bob, and looks like your next post will be a milestone or kilometre stone depending on which camp you are in.

  5. #5
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    Default

    > Given the degree of measuring of actual components does it matter if you have an
    > imperial or metric lathe for turning?

    If you are asking only about the accuracy of threads, the answer is:
    - No, if your lathe is fitted with a 127 teeth gear combination. There will be no pitch error when cutting either imperial or metric threads.
    - Yes, if your lathe is not fitted with a 127 tooth gear, you have to accept a recurring pitch error when cutting threads of a pitch system different than your leadscrew.


    > Will Imperial lathes cut metric threads and vice versa without changing the lead screw?

    It depends on the make of the lathe, and additionally it depends on the number of optional changegears that it comes with.

    > Can these be done with a change in just the back gears?

    No

    > What needs changing on a 260 with a gearbox to achieve both ?

    The 260 needs a couple of gears riveted together, in the case of the metric 260 a 63/64T gear will let you cut approximated imperial pitches. In the case of the imperial 260, a set of 60/63T gears will let you cut approximated metric pitches. Good enough to cut fastener threads, but not good enough to cut precise threads such as leadscrews.

    > Given the choice which one would you choose?

    Easy:
    - If all threads I cut were metric, I would only buy a lathe with metric leadscrew. And vice versa.
    - If most threads I cut were metric, I would buy a lathe with metric leadscrew AND a 127 tooth changegear set. And vise versa (a smaller/cheaper 63T changegear MAY be ok IF a pitch error is acceptable, otherwise it MUST be a 127T gear set)



    But there is one more important thing to consider. Can you open the half nuts to quickly return the carriage whilst cutting a thread? It can make a huge difference to ease of use:

    - On a lathe with metric leadscrew and cutting metric threads, you can open or close the halfnuts as often as you like, provided the pitch of the thread you are cutting is contained as a whole number in the leadscrew pitch. For all other pitches, you must either leave the half nuts closed until finished or you may use a thread dial if fitted. If cutting imperial threads, you must leave the halfnuts always closed - forget about the thread dials.

    On a lathe with imperial leadscrew cutting imperial threads, you can use the thread dial if fitted to open/close the half nuts. But iff cutting metric threads, you must leave the half nuts closed, forget about a thread dial.

    Chris

  6. #6
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    Sep 2011
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    Melbourne
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    Default

    Michael,

    If you want to understand thread cutting, whether it be metric or imperial, including how to cut metric threads on Imperial lathes and vice versa, do yourself a favour and buy "Screwcutting In The Lathe" by Martin Cleeve. It's available through Amazon for not many $ and it's a thorough and practical treatment of the subject. This will answer all your current questions - and then some.

    David

  7. #7
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    As usual very informative replies. Thanks.
    Part of the reason for my question is that an Imperial AT 260 is coming my way and as I already have a metric ATM 260 I am trying to decide which one to keep and which one to sell.

  8. #8
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    Springwood
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    Quote Originally Posted by dle147 View Post
    Michael,

    If you want to understand thread cutting, whether it be metric or imperial, including how to cut metric threads on Imperial lathes and vice versa, do yourself a favour and buy "Screwcutting In The Lathe" by Martin Cleeve. It's available through Amazon for not many $ and it's a thorough and practical treatment of the subject. This will answer all your current questions - and then some.

    David
    Screw Cutting in the lathe is also available from these Australian supplies

    WWW.ameng. com.au
    Plough Book Sales: Home
    MINITECH ENGINEERING AND MODEL SUPPLIES
    Dymocks bookstores. Often as shelfstock
    eBay.com.au
    Amazon gouge on postage.

    Also try AbeBooks Official Site - New & Used Books, New & Used Textbooks, Rare & Out of Print Books for new and used. Far cheaper than Amazon.

  9. #9
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    Corndale
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    Added it to the library. I ordered a few of the "Workshop Series " for Xmas reading but they arrived too late. Still a good resource for mere beginners to this type of work.
    Made a pair of Cylindrical Squares as an exercise and useful tool to go on the mill.Worthwhile to say the least. It makes you think to get this sort of accuracy .I couldn't see why both ends wouldn't be square so did it that way.The results are impressive for a newcomer.

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