Fundamental Mainspring Clarification

Discussion in 'Clock Repair' started by ChrisCam, Apr 15, 2019.

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  1. ChrisCam

    ChrisCam Registered User
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    Hi, sometimes it is good to realise how little I know and in this regard I was thinking about drum mainsprings.
    When you wind a mainspring you are creating a stored force in the spring by compressing it. The spring will have a natural inclination to unwind. So if you wind the winding arbor up say clockwise the spring will want to unravel anti clockwise. What I never gave any thought to was the fact that to use the spring to power a clock you need to fix one end of it so the force is then applied to what the spring is in contact with. Thus the winding arbor stays locked after winding via its ratchet and click spring and the drum rotates with its associated teeth driving the clock. So as I say if you wind clockwise the drum will rotate anticlockwise whilst the winding arbor remains stationary. What is of interest is why so much wear takes place on the mainspring bushes if the only rotation they receive is from winding.

    Regards
    Chris
     
  2. shutterbug

    shutterbug Moderator
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    You are mostly correct. The part that you are missing is that the winding arbor turns during winding and during running. It is under constant pressure from the spring. Therefore it usually has a much larger pivot area to overcome the natural forces against it, but still wears considerably over time. In other words, both the barrel and the arbor are turning.
     
  3. Uhralt

    Uhralt Registered User
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    I believe there is a bit of confusion. With regard to the arbor moving or not, there is a difference between open springs and springs in a barrel. With open springs, the arbor is, for example turned anti-clockwise during winding and will turn clockwise during running down. For a spring in a barrel the arbor is turned only during winding and is stationary while the clock runs down. Only the barrel turns when the clock runs down, and it turns in the direction of winding. You will often find clocks where the barrel needs to be bushed but the arbor bushing is still fine. Another extreme is a fusee. Here the arbor is stationary all the time and only the barrel turns.

    Uhralt
     
  4. ChrisCam

    ChrisCam Registered User
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    Thanks Uhralt and S.B yes the confusion is between open and drum springs as you rightly say. Also longcase weight driven clocks do have this considerable wear as the arbor turns constantly under a lot of weight.
    Chris
     
  5. David S

    David S Registered User
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    And I have found that long case clocks that use a crank instead of a traditional key can have lots of wear around the winding arbour do to the "wallowing" effect as you turn the crank.

    Here is a pic of one that was so bad the teeth were being compromised. Note the brass fillings on the stop works below.

    time winding bridge wear close.jpg

    David
     
  6. ChrisCam

    ChrisCam Registered User
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    Yes get your point its almost like using the arbor as a crude broach.
    chris
     
  7. shutterbug

    shutterbug Moderator
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    David - I have one of those on the bench, and have that big washer on wrong. Thanks for the pic!
     
  8. David S

    David S Registered User
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    Hey Shutterbug that is great news. Was the winding arbour bridge worn badly on yours?

    David
     
  9. shutterbug

    shutterbug Moderator
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    Fortunately, no. Snugged down nicely with very little slop.
     

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