Correct Harrison maintaining power spring tension

Discussion in 'Clock Construction' started by Phil Burman, Sep 28, 2017.

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  1. Phil Burman

    Phil Burman Registered User

    Mar 8, 2014
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    I’m hoping somebody can give me some insight into the correct spring tension for a Harrison maintaining power arrangement under normal running.

    Should the spring tension hold the ratchet wheel hard over against the great wheel stop during normal running or should it only partially compressed the spring and be floating. Floating would give the same (correct) tension as provided by the fuse cable and therefore appears to be the correct setup but wouldn’t floating have the ability to provide unwanted variable tension during normal running?

    Any insight would be most appreciated.

    Phil
     
  2. John MacArthur

    John MacArthur Registered User
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    Feb 13, 2007
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    Since nobody else has popped up, I'll stick my neck out. I would say that ideally, the springs should be over to the stop, but just barely. This would mean that you'd have nearly the tension that you'd normally have, and wouldn't be at the limit of the springs. Mine are set to the stops, and don't provide quite a normal amount of drive, but I only expect them to keep the clock running forward while I'm winding it. This is such a small amount of the week that I'm not worried about keeping exact pressure on the train, but rather don't want to lose the time that I'm winding it.

    Johnny
     
  3. Phil Burman

    Phil Burman Registered User

    Mar 8, 2014
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    Thanks for the input Johnny, it is much appreciate. It is my understanding that when aiming for absolute maximum precision it is necessary to eliminate every possible source of disturbance to the pendulum movement, however small. I can see this with the Microset timer. After winding, the pendulum takes a while to settle down and very often at a slightly different rate, I will take your advice and set the spring so it is barely on the stop and see how it performs. I think until now the spring has been far to weak. I guess finding the right strength is going to be a lot of trial and error.

    Phil:)
     
  4. John MacArthur

    John MacArthur Registered User
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    Feb 13, 2007
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    You're welcome - I for one will be interested in the outcome of your experimentation.

    Johnny
     
  5. jhe.1973

    jhe.1973 Registered User
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    Feb 12, 2011
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    Hi Phil,

    My two cents worth is to agree with Johnny, both as to the stop question and to being interested in your results.

    The Microset sure does make 'tuning' easier......while showing us that perfection in a mechanical clock will always be be out of reach.
     
  6. Phil Burman

    Phil Burman Registered User

    Mar 8, 2014
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    I’m not sure I would dignify my investigation with the word experimentation however here is some feedback on what I did. I performed the “experiment” using my “Allan Wolff” skeleton clock, which uses a piece of piano wire bent at an angle and with a fixing loop on each end (see photo below - from Allans' skeleton clock build manual). The installed force provided by this spring arrangement is dictated by its:

    1) Yield strength and modulus of elasticity (MoE) of the spring material

    2) Wire diameter

    3) Spring length (loop to loop)

    4) Uncompressed angle between the two spring arms.

    Spring steel is the logical and possibly the only practical choice for this configuration and application and spring length is largely dictated by the available space. This leaves wire diameter and uncompressed angle. Angle can be varied within a single spring whereas wire diameter requires the making of a new spring.

    So my approach was to guess the necessary wire diameter (as per Allans’ clock – 1.2mm) then test the spring at maximum and minimum angles, for this I decided on 50 degrees (again as per Allans’ clock) to a maximum of 120 degrees. When I checked the performance for both of these angles the spring was full held against the stop by the main spring for both angles. This indicated that the wire diameter was too small. Next I tried 1.6mm at 120 degrees, this spring held the main spring hard against the other stop under normal running which indicated that the spring force was too great so I reduced the spring angle to approximately 85 degrees. At this setting the wire spring was held against the stop by the main spring and managed to keep the clock running during winding, although it seemed a little weak. This seems to be the correct setup although at little more angle might help, however I left it as is for the moment.

    phil

    Allans maintaining spring.JPG
     
  7. WMello

    WMello Registered User

    Jan 30, 2016
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    Hi Phil, thank you for the post.

    I'm struggling with the maintaining spring on my project. I was unable to get good results following the instruction on the plan.
    John Wilding's plan calls for a 1/16" square section of tool steel wire, to be annealed, formed, hardened and tempered.
    Tried several times and got permanent deformation, or breakage. In the end I've settled for a standard round section of music wire bent to shape.
    I've learned about stress relief for sprints made this way with music wire (500°F, 30 minutes). Don't know if it's necessary.
    As the click is still under construction there is no way to fully test it now, but it is a case of concern for the future.

    Wagner
     
  8. Phil Burman

    Phil Burman Registered User

    Mar 8, 2014
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    I was going to comment on the design of your maintaining spring if it were not for the fact that my lack of clock experience usually gets me into trouble when I do.

    From an engineering view point the section of spring wrapped around the great wheel boss will have very little input to the operation as that section will be constrained by the boss when there is an attempt to compress the spring. For it to work the radius of that section of spring needs to be somewhat greater than the boss radius in order to avoid contact, otherwise it is likely to deform or break close to where the longer arm meets the boss. Also getting the tempering exactly right without a temperature controlled furnace can be tricky for highly stressed springs. If the tempering temperature is to low the spring breaks in use, to high and it deforms.

    Phil
     
  9. Phil Burman

    Phil Burman Registered User

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    PS: it is a nicely shaped spring though.

    Phil
     
  10. WMello

    WMello Registered User

    Jan 30, 2016
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    Yes Phil, that spring in the post #10 was useless.
    Skeleton Clock
    I figured out about the inner radius problem. The description on the plans are vague and there is only a couple of black and white grainy pictures.
    The one in use now is different. Round section music wire, larger radius and no hardening/tempering.

    Wagner
     

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