Thread Pitch on 8mm Chuck

Discussion in 'Horological Tools' started by KurtinSA, Jun 1, 2018.

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  1. KurtinSA

    KurtinSA Registered User
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    Nov 24, 2014
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    I purchased what appears to be an 8mm 6-jaw chuck at an estate sale...diameters match the 3-jaw that I have. I'd like to see about cleaning up the threads on this new chuck. What is the size needed in order to clean these threads up? The diameter of the solid portion of the shank is 8mm, but the diameter across the threads is 6.7mm.

    Thanks...Kurt
     
  2. KurtinSA

    KurtinSA Registered User
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    Nov 24, 2014
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    Found out they're buttress threads...not sure exactly which kind. Only a special die would work. The threads weren't that bad...I just cleaned them up some brake cleaner and a toothbrush.

    Unknown 10mm lathe

    Kurt
     
  3. wefalck

    wefalck Registered User

    Mar 29, 2011
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    Are you sure they are buttress threads ? Never heard of any such thread on 8 mm-collets. Normally the thread is 6.8 to 6.9 mm diameter and 40 TPI, symmetric.
     
  4. KurtinSA

    KurtinSA Registered User
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    Nov 24, 2014
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    I did measure approx. 6.7-6.8 mm across the threads. I'm no machinist...I was just told they were buttress threads. I tried using my loupe to look at the threads...hard to tell, but they might just be symmetric.

    BTW...no manufacturer that I can find on this chuck.

    Kurt
     
  5. wefalck

    wefalck Registered User

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    I gather the key question would be: does it fit the draw-tube of your lathe ? Or, would it fit the draw-tube for other known lathes ?

    You could count the number of threads per inch (or per centimetre). The pitch of thread for all 8 mm-lathes seems to be 40 TPI. The diameter, however, varies between 6.68 and 6.85 mm from manufacturer to manufacturer. A smaller diameter collet fits into a larger draw-tube, but obviously not vice versa. You can measure the collets you have, if they are larger than the shaft of your chuck, you should be lucky. If they are smaller than the shaft of the chuck, you may need to get a thread-chasing die of the right diameter for your lathe. With this you can reduce the thread diameter of the shaft of your chuck. These dies can be now found a quite reasonable price on the Internet and are useful for cleaning up threads anyway.
     
  6. KurtinSA

    KurtinSA Registered User
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    Nov 24, 2014
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    Thanks...the chuck fits the draw tube of my Levin lathe. It was when I first used it without any cleaning, it didn't seem to draw up tight enough. I used the toothbrush and a cleaner on the threads and it seems to work better. I have a 3-jaw chuck but wanted to try a 6-jaw to see how it might work.

    Kurt
     
  7. trim

    trim Registered User
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    Feb 19, 2010
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    WW should be 0.275-40 and are sold each and every day on ebay. The RDG ones are very nice.
     
  8. wefalck

    wefalck Registered User

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    ... should be, but If you have a look at the table in Carlè's book, you will see that the diameter varies from manufacturer to manufacturer.
     
  9. flynwill

    flynwill Registered User
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    I created this page in our "encyclopedia" some time ago: https://mb.nawcc.org/wiki/WW-Collets
    There are both 40 TPI thread and 0.625mm pitch (40.64 TPI threads), and also 0.75mm threads on the new ones from the Orient.
     

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