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  1. #1
    Join Date
    Jul 2008
    Location
    near Warragul, Victoria
    Posts
    3,718

    Default Book: Screwcutting in the lathe

    Martin Cleeve

    This book is full of tables , formulas and much information .

    But, the author has a obvious dislike of Norton QC gear boxes . He writes , in his opinion they limit the choice of threads available . The book completely ignores any methods or descriptions of using a QC gearbox.

    The book seems pretty useless to anyone with a QC gearbox, because the formulas and tables he has are fine for a lathe without a Qc gearbox. How do you convert all of his work into a lathe with a QC gearbox lathe ?

    Mike

  2. #2
    Join Date
    Oct 2011
    Location
    Norwood-ish, Adelaide
    Age
    59
    Posts
    6,540

    Default

    I must admit that was the impression I got from the book too. I felt that he thought QC boxes were lowering standards - but then he was running a business using a highly modified myford lathe, so he had some unusual ideas himself.
    Your lathe should have a chart showing the gears to get the various pitches available from the gear box. Failing that you may have to experiment a bit - that is (under hand power), set up clocks or calipers to measure how far the carriage moves for one revolution of the spindle (or alternately, to move the carriage one inch, how many revs of the spindle are required).

    Michael

  3. #3
    Join Date
    Apr 2009
    Location
    Kingswood
    Posts
    930

    Default

    Mike,
    On the QC gearbox will be a table specifying the input gears to be set on the quadrant and the resultant thread cut for each setting.
    Use Martin Cleeve's data to calculate the thread assuming the QC gearbox is 1:1 and then compare with the actual value produced - the difference will be a constant factor for that QC setting.

    Each QC setting will have a different factor that can be recorded next to the QC gearbox.

    Then, just apply Martin's approach introducing the additional factor for each QC setting, as though it was an additional gear pair on the quadrant.

    Note that one of the QC settings will be 1:1, and it could be left in that position whenever Martin's data is to be applied.

    John.

  4. #4
    Join Date
    Jul 2008
    Location
    near Warragul, Victoria
    Posts
    3,718

    Default ratios

    Hi John

    Yes my Sheraton has a 8 tpi lead screw . If I set the QC gearbox to cut a 8 tpi thread , I assumed it would be set at a 1:1 ratio , but I don't think that is the case .

    For the normal imperial setup , the stud gear is 20 teeth and the QC gearbox gear is 56 from memory . The middle idle gear doesn't affect the ratios at all ? If the QC gearbox was a true 1:1 ratio at 8 tpi , then the stud and QC gear would have the same number of teeth ?

    I might be talking crap

    Mike

  5. #5
    Join Date
    Apr 2009
    Location
    Kingswood
    Posts
    930

    Default

    Mike,
    I have a Sheraton 9A with 8tpi leadscrew.
    A few years ago I stripped down the QC gearbox for an inspection and clean.
    On this gearbox there is no setting that provides 1:1.
    With 20 T on the stud gear and 56 teeth on the gearbox input, the reduction spindle to gearbox input is 20/56 = 1:2.8.
    QC set to A-1 has a speedup ratio of 2.8:1.
    The combination gives a 1:1 spindle to leadscrew and a thread of 8 tpi is generated.

    From the above you can calculate what each gearbox combination provides.
    I counted the teeth on all the gears and confirmed that the engraved table is correct.
    A-1 to A-8, and B-1 to B-4 are all speed-up ratios, the remainder are reductions.
    E-8, for example is 0.1.

    I will document all the QC gearbox ratios during the weekend and provide it as a table of values.
    I have no idea if the Hercus is the same.

    John.

  6. #6
    Join Date
    Apr 2009
    Location
    Kingswood
    Posts
    930

    Default

    Mike,
    The attached xls file lists all the Sheraton 9A QCGB ratios.

    I was interested in the actual ratios as I investigated cutting metric threads without using a 127 gear - got quite good approximations that I used several times.

    With a bit of luck, my Sheraton should be back in use by the end of the year.
    John.

  7. #7
    Join Date
    Jul 2008
    Location
    near Warragul, Victoria
    Posts
    3,718

    Default great

    I saved that to a memory stick

    I am certain the HERCUS 9A imperial set is the same as Sheraton, so your table will help out other owners .

    Thanks

  8. #8
    Join Date
    Aug 2008
    Location
    near Rockhampton
    Posts
    6,216

    Default

    Quote Originally Posted by morrisman View Post
    But, the author has a obvious dislike of Norton QC gear boxes . He writes , in his opinion they limit the choice of threads available . The book completely ignores any methods or descriptions of using a QC gearbox.
    Sounds like some old stuck up Brit..
    Gold, the colour of choice for the discerning person.

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