Why use a Compound Pulley System on a Tower Clock ???

Discussion in 'Tower, Monumental & Street Clocks' started by keinert, Nov 29, 2013.

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  1. keinert

    keinert Registered User

    Apr 30, 2012
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    I see many youtube videos where the time and/or strike weights are hanging from a compound pulley system. What's the advantage of doing this compared to not "compounding" at all?

    Logic dictates that the weights would need less vertical room if you compound the pulleys, but then you'd be required to use more weight.

    So, is the amount of "compounding" used in each tower clock installation a trade off between how much vertical height you have for the weights to move verses how much weight you can afford to buy?

    Thanks,
    Kevin.
     
  2. leeinv66

    leeinv66 Moderator
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    It is all to do with run time. If you have the room for the weights to fall without a compound pulley set up, then that is what you would do. If you don't have the room available to achieve your desired run time, then you use a compound system. The trade off being you need to hang more weight.
     
  3. doug sinclair

    doug sinclair Registered User

    Aug 27, 2000
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    I doubt very much that price of buying weights would predicate how much the system was compounded. I have seen images of clocks that use a box of rocks for weight. Available, and cheap. The total fall available for the weights would the biggest factor. This would probably be based on winding once per week. That is, assuming the clock is still wound by the "armstrong" method. If electrically wound, depending on the fall available for the weights, compounding may or may not be necessary. If compounding means you can get by with winding once per week, rather than twice, I suspect compounding would be the way to go.
     
  4. keinert

    keinert Registered User

    Apr 30, 2012
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    Hey guys, thanks for your answers! I measured my strike drum diameter after posting this question and the reason for compounding is obvious now. If I want to wind once each week, I need 69 feet of fall !

    -KK
     
  5. doug sinclair

    doug sinclair Registered User

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    Using the current weight dedicated to the strike side, and considering a fall of 69 feet during a one week run, I feel that a single pulley should work. The fall then should be 35 feet, but you'll need twice the weight. Compound it twice, and you should have a 17-foot fall, but three times the weight, the way I figure it.
     
  6. Donn Haven Lathrop

    Donn Haven Lathrop Registered User

    Jul 28, 2010
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    Doug: Semantics. Just what does "compound twice" mean? A compound system has at least two suppporting strands (or FALLS [the preferred term]). Does "compound twice" mean four falls? Three falls? How many? Go to: http://www.sover.net/~donnl/cables.html for wire rope terminology and handling.
     
  7. prideofmatchingham

    prideofmatchingham Registered User

    Dec 13, 2011
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    Hi Donn, you link is not working.

    This topic is of special relevance to me. Have got a Turret clock restored and installed in my drawing room between two cubboards so that the sspace is used for the weights to descend. But the height being only five feet, it needs almost every 32 hour winding. How do I solve the problem and make it atleast five to 7 days?

    Here are the pics
    DSC03637 (1024x768).jpg DSC03638 (1024x768).jpg TC8.JPG

    Thanks
    POM
     
  8. gvasale

    gvasale Registered User
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    Brace the ceiling & run the cable to it. You can experiment from there. Larger diameter round discs can pick up a few hours by shortening the height of the weight stack.
     
  9. prideofmatchingham

    prideofmatchingham Registered User

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    Have to be careful about the strength of the ceiling/bracing lest it should give way and weights fall abruptly. Any list of precautions to be taken?
     
  10. gvasale

    gvasale Registered User
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    How much weight are you using? If it's not too great, it ought to be relatively simple. What type of building construction?
     
  11. Tinker Dwight

    Tinker Dwight Registered User

    Oct 11, 2010
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    The wire you currently have looks real thin for the weight
    you have hanging.
    Just my thought
    Tinker Dwight
     
  12. prideofmatchingham

    prideofmatchingham Registered User

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    Weight is 15 KGs. Ceiling typical cement mortar and bricks. Though I guess a fan must also be weighing roughly the same!
    As for the dia of the wire, it has been ticking away for many months and is a real strong wire made of many thin steel wires wound around. Would you like to know the dia?
     
  13. gvasale

    gvasale Registered User
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    Thinking Mumbai (Bombay), is this an apartment building? Do you have a way to securley anchor it into the ceiling? If not, some kind of wood or metal framework to support the weight and fasten to the wall so it won'f fall would work very well. The photo looks like it weighs more than 33lbs (15kg.)

    It would be interesting to know the diameter of the cable, which by your description is actually wire rope.
     
  14. Jim DuBois

    Jim DuBois Registered User
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    In order to get a 7 day run it would appear you need to run the weight over a pulley at ceiling level, as well as compound the "fall" of the weight, and the compound would seem to need a compound of 3 or 4 unless you have some very high ceilings....to that point I had an E Howard street clock that I triple compounded with a weight of 48 pounds (22 kilos), and it barely ran. To triple compound your mechanism you would need a drop of about 75" (191 cm+/-) and a weight of maybe 35 kilos (guess I don't know if your clock actually requires 15 kilos to run with no compound, I suspect it does not)

    As pictured in the photo triple compounding this little clock only ran a couple of days, but as a shop focal point that was ok when it was finished...
     

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  15. harold bain

    harold bain Registered User
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    I suppose another possibility would be to cut a hole in the floor to allow a longer weight drop. If you have a basement, you could build a hollow column to receive the weight.
     
  16. FDelGreco

    FDelGreco Registered User
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    POM:

    The first thing you need to do is to figure out how much drop you actually need to run the length of time you want. First, determine how many hours you get from one turn of the winding drum. The length of cable for that length of time is the diameter of drum x 3.141. Then calculate total cable length (drop) for a noncompounded weight.

    Example: Drum is 3” in diameter and one turn runs the clock for 4 hours. 3 x 3.141 = 9.423” of cable for four hours. If you want to run the clock for 5 days (120hours), then 120/4 x 9.423 = 282.69” or 23.6 feet. That’s a really tall room if you just want to attach a pulley to the ceiling. To that length you need to add for the pulley hanger and also the length of the weight – perhaps a total of another foot or so. Such a situation will probably require multiple compounding.

    Do the calculation for your situation and let us know. On the other hand, clockmakers made 30 hour clocks for centuries. I have a 30 hour wag on wall from 1880s that I wind every morning.

    BTW – the minute hand on the clock is too long.

    Best regards,
    Frank
     
  17. prideofmatchingham

    prideofmatchingham Registered User

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    Frank thanks for detailed reply. And sorry for the minute hand! Never got around to clipping it a bit. Next picture would show the correct minute hand. Presently occupied with Gents Leicester C7 Pulsynetic Master clock!!!
     
  18. Donn Haven Lathrop

    Donn Haven Lathrop Registered User

    Jul 28, 2010
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    <Quite>Hi Donn, your link is not working.</Quote>

    Yes, it is working.

    One thing no one has mentioned in all the talk about compounding the weight falls. The clock may well need only 15 KG to run for approx 32 hours. With 168 hours in a week, the immediate requirement is that to achieve a weeks' run, the falls will have to have six supporting strands. Of course, that means that the weight has to be six+ times heavier because of bending loads in the wore rope, pulley/sheave friction in the compounding plus whatever friction comes from redirect pulleys. From experience, you can expect at least a 3% friction load from each pulley. Do NOT forget that while the clock "sees" only the 15 KG necessary to run it, the ceiling sees, in this case 6 times 15 KG, or 90 KG, PLUS the additional weight needed to overcome friction and bending loads.

    Make sure the ceiling will support the 90++ KG, or trouble will ensue.
     

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