Threads on a Pultra

Discussion in 'Horological Tools' started by Britannicus, Sep 25, 2017.

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  1. Britannicus

    Britannicus Registered User

    Apr 26, 2016
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    I'm trying to find an adapter for my 8mm Pultra - these seem about as common as rocking horse droppings !

    I saw this Boley 8mm adapter and wondered if it would fit

    A bit of research on WW collets (Robert Bastow) suggests it might be

    "I say this because it is known that the WW threads are originally an anglicized
    version of the original 8mm European sizes..of which there are MANY..most of
    which are interchangeable with WW collets, drawbars etc.

    It is also known that, in order to facilitate this interchangeability..drawbar
    threads are purposely cut to maximum sizes

    Thus, if you have a drawbar tapped to the above spec..either .275-40 tpi H2 or
    the equivalent metric size 6mm x .625mm you can use WW or 8mm collets in it from
    all the following manufacturers..my sizes are taken from "the Model Engineers
    Handbook" by ..Tubal Cain..the other guy..the REAL ONE as someone said!!

    8mm collets from Adams, Boley, Boley-Leinen, Coronet, Derbyshire, Pultra and WW
    are all threaded 0.268-40 and will all be a fairly sloppy fit in your
    drawtube."
    Has anyone real experience with this ? to establish if this does work ? s-l500.jpg

    s-l64.jpg
     
  2. Moebius

    Moebius Registered User

    Jan 3, 2009
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    I have a Pultra 10 (8mm) and a Star 8 mm (--> 6.82 mm thread)
    I can use both collets on either lathes. Schaublin or Bergeon do fit ok as well.
    Boley or Lorch cannot be used on these lathes.


    From the tables I've read, the WW collets can't be used on a Geneva lathe. I've never actually tried, so I may be wrong.
     
  3. Britannicus

    Britannicus Registered User

    Apr 26, 2016
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    Thanks for the input - I'm trying an alternative approach for the moment - I've ordered a new 8mm drawbar with a WW thread - hopefully this will work for me - I'll keep you posted
     
  4. rstl99

    rstl99 Registered User
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    Interesting. I just acquired a Star 8mm lathe (7a model). It came with mostly Star collets but several other ones without markings on them. From the collet reference table in De Carle's book on lathes (which he admittedly pulled from Crawford's, a UK manufacturer of split chucks, lists the following lathes as being compatible (exact fit) with the Star for collets:

    Cowells 8mm
    I.M.E. 8mm
    Lane Cove (Lanco) 8mm
    Lorch 8mm
    Nordan
    Reliance
    Swan 3 in.
    Taylor 8mm

    The Bergeon specs are close but not exactly the same as Star's. Ditto for Pultra. But sounds like they fit well based on your experience, which is good to know.

    I recently corresponded with someone at Star SA, and he said the collets in the Star are "B8", which he claimed are "the same in all 8mm lathes, Bergeon, Lorch, etc."

    Hope this helps.
    --Robert
     
  5. Moebius

    Moebius Registered User

    Jan 3, 2009
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    Then you may have spoken with Mr. Gentil @ STAR.

    I tried a few Lorch collets, it never fit well. Maybe it can fit if you're screwing the drawbar with overpowering force, but I do prefer to play it safe and keep the threads nice and clean ;)

    And interesting question to ask to Star SA would be "are you making the collets by yourself or is it made by another company and rebadged ?".
     
  6. rstl99

    rstl99 Registered User
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    Oct 31, 2015
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    Yes, I was corresponding with Mr. Gentil. He does not respond very quickly (if at all) but then again he is the manager of the company I believe.
    I would not be surprised if the collets are rebadged from another maker, but will ask him if I hear back from him on a question I posed about a missing part on my lathe (index pin? to lock the lathe on one of the holes on the "index wheel" that's part of the pulley?).
    It's nice in a way to have a tool from a company that still makes them, but buying any new or replacement item from them would likely be pretty expensive...

    Good to know about Lorch collets, thanks for sharing. Indeed, one needs to care for these collet threads and not over-tighten. At least that's one thing I learned from my readings...
     
  7. Britannicus

    Britannicus Registered User

    Apr 26, 2016
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    Well, I took a bit of a gamble and sent off for a M12x1 adaptor for a Boley lathe. I just tried it in my M10 8mm Pultra (always confused why the 8mm was called the M10 model when they produced a 10mm machine ). I'm pleased to say it fits the draw bar beautifully - so I can now run my lathe with a metric chuck as well as pultra fittings :) :)
     
  8. wefalck

    wefalck Registered User

    Mar 29, 2011
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    'B8' is a denomination used by Schaublin (as is 'B6'). B8 collets would fit almost any of the Swiss equipment from Bergeon, Dixi, Hauser, etc. and, of course Schaublin itself. B8 collets also seem to fit well draw-tubes from Lorch, Schmidt & Co. and Wolf, Jahn & Co.

    Lorch seems to have slightly modified their specs for the collet thread over the years, as I found that some collets don't fit the B8 draw-tubes, while most do.

    It seems that the German firm Ortlieb (which is still in business) made collets for many know lathe manufacturers, such as those named above.

    Of course, WW-collets can be used on a Geneva-style lathe - provided that is an 8 mm and not a 6 mm one, and that you have a suitable draw-tube.

    Incidentally, I recently purchased a couple of those Chinese 12x1 adaptors and found that they seem to have some manufacturing tolerances. One fits my Lorch WW-lathe cum draw-tube perfectly, while the other one does not fully enter the headstock (but the thread is ok). I have not fully investigated, but either the shaft diameter is a tad to large, or the slot for the driving pin is too shallow.
     
  9. Britannicus

    Britannicus Registered User

    Apr 26, 2016
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    Interesting - thanks for your comments. I have on order a WW draw tube which I hope will further give me some options -
     
  10. Moebius

    Moebius Registered User

    Jan 3, 2009
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    That was almost 2 years ago... but what was the result with the WW draw tube ?
     
  11. Britannicus

    Britannicus Registered User

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    Yes - it worked extremely well :)
     

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