Suspension spring mounting detail

Discussion in 'Clock Construction' started by dandydude, Aug 29, 2015.

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  1. dandydude

    dandydude Registered User

    Nov 30, 2014
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    Hello,

    I have come across different details for mounting the suspension spring in precision clocks. Some have a screw above the top chops (Blocks that hold the springs together). Are these screws to make sure the spring is exactly vertical?

    Is this really necessary? Cant the top chops be pivoted so that gravity and weight of the pendulum would make sure the spring is vertical? I did also observe that some pendulum rods are suspended by means of a hook from the bottom chops. Some are just screwed directly to the bottom chops. Again isnt the hook better as it also acts as a pivot to make sure the pendulum rod is absolutely vertical?

    Thanks
    Dandy
     
  2. Tinker Dwight

    Tinker Dwight Registered User

    Oct 11, 2010
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    For best results you can have it pivot by its own weight
    and then lock it down with a set screw. That will give
    the best results. If it shifts a little while running, it can make
    minor upsets and erratic upsets to the rate.
    Tinker Dwight
     
  3. dandydude

    dandydude Registered User

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    Dear TD,

    For the crutch adjustment, I would rather move the pendulum assemble with a leadscrew. What do you think of an arrangement as shown in my sketch.

    Thanks
    Dilip WP_20150829_001.jpg
     
  4. Jim DuBois

    Jim DuBois Registered User
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    Dilip, it is advantageous to keep the point of suspension of a pendulum assembly ABSOLUTELY rock solid if the goal is to achieve maximum accuracy of time keeping. I don't believe that can be done in the general approach you have in your drawing. Even if the movable portion of the assembly was on a robust sliding dovetail with a spring loaded gib in a heavy/massive steel frame it would seem that the necessary rigidity would still be difficult to achieve. Keeping it simple is still often the best solution in my opinion. A very robust solution that could be made for a precision clock can be seen in something like and E Howard tower clock. The fine rating nut is found on the top of the suspension spring. The suspension spring rides between 2 chocks that control the point of flex for the spring, ultimately determining the rate of the pendulum. It is adjustable without stopping the pendulum. The beat adjustment on these clocks is adjustable between 2 screws on the crutch, also, can be set while the clock is running, with very minimal disturbance to the timekeeping. These tower clocks have been built this way since about 1847, perhaps longer than that. It is simple, robust, and lends itself nicely to precision timekeepers. I have built a couple of clocks using these methods and have had a number of tower clocks over the years with these devices, so I can speak to their robustness and accuracy. The photos show both assemblies used in a 0 sized Howard clock, but such an approach can be cleaned up considerably and used in a precision clock in my limited experience. I really do prefer simple over complex and this approach will achieve the accuracy I have needed so far.
     

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  5. dandydude

    dandydude Registered User

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    Dear Jim,

    How does the spring assembly move up and down? Do the top chops have a threaded hole through them?

    Thanks
    Dilip
     
  6. Jim DuBois

    Jim DuBois Registered User
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    Dilip,

    yes, the suspension spring is moved up and down by a threaded rod and adjusting nut on top of the assembly. This is the fine adjustment for timekeeping on these with the "rough setting on the bottom of the bob. The intent is to get the clock keeping decent time using the rough setting then tune it with the rating nut on top. Some of them are pretty finely calibrated with a scale that may reflect just a few seconds a week per division on the scale. The range of adjustment on the length of the suspension spring is less than 1/4" so the rough adjustment needs to get the timekeeping close to final length. Obviously, using a finer thread and a larger dia finer resolution scale much more precise adjustments could be made on a precision clock. For your purposes it might be necessary to refine this a bit, but the approach is very valid IMO, and it is simple enough that there is a good likelihood of creating a very good timekeeper without requiring a master machinist..
     

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  7. dandydude

    dandydude Registered User

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    Dear Jim,

    Thanks a lot for the images.

    Dont a lot of precision clocks have a pivoted top chop with on 'v' grooved bracket. Wouldn't that be even sturdier? But of course at the cost of a fine adjuster.

    Thanks
    Dilip
     
  8. jhe.1973

    jhe.1973 Registered User
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    Hi Dandy,

    A suggestion I have, if you choose the approach that Jim has shown, is that one side chop, shown screwed to the circular, slotted mount, would be a solid part of this circular mount. Only one chop would be movable and it would have a screw to clamp it and the spring to the non-movable side after each adjustment.

    Jim, I like so many of the photos that you post and have saved a lot of them.

    Thanks so much, but why not save me some time and just send me all the photos you have?

    :whistle: :screwball::D
     
  9. Jim DuBois

    Jim DuBois Registered User
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    Thanks for the good words on the photos. I can think of a couple of reasons you might not want all the photos I have. First, I am one of the worst photographers in the world. Second, last time I looked I had about 50 GB's of clock related photos....and to add insult to injury my naming and filing habits have no protocols nor conventions...sadly.....in this case it was pretty easy, the T&S Howard tower clock sits unloved in my garage, so details are readily available. Also, I have maybe a ton of other tower clock parts in the garage.....and I have been making clocks for 45 years so I have photos of lots of things I found of interest. Too bad I didn't have a digital camera when I started. I would most likely now have 200 GB's of photos....and still no convention....
     

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