Center shaft collet - spring tension on minute hand arbor

Discussion in 'Clock Repair' started by THTanner, Dec 11, 2018.

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  1. THTanner

    THTanner Registered User
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    Jul 3, 2016
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    I have read a bunch about replacing these collets with properly sized bushings, or finding similar collets in a variety of sizes (which so far I have not been able to find), but I am wondering about replacing it instead with a longer collet with a set screw.

    I am not sure how this one split, but the clock came in with the complaint that the minute hand just spun freely so it happened somehow while the movement was assembled, or perhaps it just finally worked loose.

    The small collet looks slick as opposed to how a longer one with a set screw would appear, but I don't see any other draw back. Any experience or issues with this change?

    IMG_3103.JPG
     
  2. R. Croswell

    R. Croswell Registered User

    Apr 4, 2006
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    I guess the best solution would be to make a new collet that fits tighter. Short of that, if you calculate where it is supposed to be and drill a hole through the arbor carefully located where you can insert a tapered pin after the collet is pressed into place. The pin then driven home tight should work. Make sure the collet isn't actually cracked. If it is, the only solution is a new one.

    RC
     
  3. THTanner

    THTanner Registered User
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    Totally cracked - can't see it a photograph - at least not with my equipment - but it catches the fingernail as you turn it and it slides and rotates with no effort.

    I was just wondering about the set screw approach that I saw mentioned in an old post. I worry about it working loose over time.

    The tapered pin might be easier to work - with shim washers to get the correct tension - thanks
     
  4. Willie X

    Willie X Registered User

    Feb 9, 2008
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    A #26 Bergeon bushing (or similar) and a few minutes with the ole 5 sided broach will do it. Willie X
     
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  5. kinsler33

    kinsler33 Registered User

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    It's not clear which 'collet' or whatever is being discussed here.

    I just got done with a classic Gilbert whose cannon pinion was cracked (right through the entire length of a tooth, mind you) _and_ the weird face-cam in the
    speed regulator was cracked as well. About all I can think of is that there is some variety of brass that shrinks over time, and that's what Gilbert used in his clocks.

    I'm quite confident in using permanent Loctite to secure these, for they're not under any particular stress and it's easy to clean the surfaces prior to the application.

    M Kinsler
     
  6. THTanner

    THTanner Registered User
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    This is the collet on the center shaft of a Sessions mantle clock. This is from a boneyard movement from which I took parts to repair the movement with the bent arbor for the verge. The collet puts pressure on the spring to provide tension for the minute hand. It is just a learning project for me in the various ways to repair this. Other posts on the board discuss various techniques and I was wondering about experience with a longer collet with a set screw. Exact collets don't seem to be available so they have to be made or a bushing modified to fit tight. I will probably try different methods and to learn a bit.
     
  7. shutterbug

    shutterbug Moderator
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    A set screw would be overkill in this application because there would never be a need for it. I agree that a new bushing is the way to go, and put it back like it was originally.
    I think Gilbert just made the holes too small and forced the pinion into place with brute force. The replacement pinions are also too tight, and I usually ream them out a bit before putting them on the arbor.
     
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  8. R. Croswell

    R. Croswell Registered User

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    A "longer collet" might be stronger and less likely to crack. There are several problems with set screws, first is that the collet has to be secured while the tension spring is compressed which presents the challenge of holding the collet against the spring while tightening the set screw. For the best grip one would use two set screws ant 90 degrees. Seems like a lot of extra work. Loctite presents the same challenge of holding the collet under tension against the spring until the compound cures. I wouldn't recommend Loctite for this, especially if the cracked collet is reused. I can't recall ever having a problem with this collet on a Sessions movement and I see no reason to change the original design. Just make a new collet, a bit more robust if you like, with a tight press fit and press it on until the tension spring has the right tension and job done. If there is anything to be learned here it is perhaps the advantage of own a small lathe on which a part like thic can be made in just a few minutes.

    RC
     
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  9. THTanner

    THTanner Registered User
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    that will be the final result I am sure - but as with any experiment there are no failures, just lessons of what is not a good idea :)
     

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