Using just one weight on a two weight Seth Thomas movement

Discussion in 'Clock Repair' started by THTanner, Mar 13, 2017.

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  1. THTanner

    THTanner Registered User
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    Jul 3, 2016
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    I am designing a clock to go into a display cabinet for a customer. The movement is a Seth Thomas time and strike weight driven movement from a case that is unusable. I have the original face and suitable hands and the client likes all of that. But, they have asked if I can use just one nice looking brass covered weight that hangs in the middle instead of the usual two lead weights that hang to each side.

    The rough drawing below shows what I am thinking of trying. During a short sequence strike it should not be a problem. But on a high hour count strike I suspect the effective weight on the time side might drop enough to slow or stop the pendulum as the weight falls rapidly to power the strike.

    This could be overcome by using a somewhat heavier weight, but I am concerned with putting too much weight on the movement. I know some of these work fine with as little as 6 pounds each side and most run closer to 8 pounds. Any idea what a safe upper limit might be for the weight on each side of one of these?

    thanks
     

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  2. David S

    David S Registered User
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    Dec 18, 2011
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    What is the model of the seth Thomas? I am working on a T&S Seth Thomas 30 hour that has 3 lb on the time and 2.5 lb on the strike.

    David
     
  3. THTanner

    THTanner Registered User
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    This is an 8 day Seth Thomas Lyre movement that has 8 pounds for the time and 8 1/2 for the strike. But they are the rectangular lead weights. The display case has glass sides and a mirrored back so they will be able to see the movement and don't really care for the look of the old weights.

     
  4. Willie X

    Willie X Registered User

    Feb 9, 2008
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    Sure, but you will need a weight around 16 pounds and you probably won't have enough room (about 3") for a cylinder shaped weight, unless it is very long.
    You will also need around 18 inches of extra case height for an 8-Day runner and the pendulum is going to be way to short for this case length.
    I think the weight cord will pull off the outside of the drums.
    Willie X
     
  5. novicetimekeeper

    novicetimekeeper Registered User
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    I don't understand how you wind it, do you just do equal winds on each greatwheel? I have lots of single weight clocks using the Huygens continuous drive system but the weight drops 5-6 feet in 24 hours.
     
  6. THTanner

    THTanner Registered User
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    The plan is to add the little lever that follows the cable as it is wound onto the drum to indicate when each side is full.

    - - - Updated - - -
     
  7. THTanner

    THTanner Registered User
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    Yes - about 16 pounds. It is a tall, floor display case so the extra height is there. It may look funky though with the 15 inch pendulum which will have to swing between the cables so the weight will not be wound up too close to the movement. I am trying to convince them to use two 8 pounders in brass sleeves hanging on either side as usual.

     
  8. Willie X

    Willie X Registered User

    Feb 9, 2008
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    Separate weights will be much less problematic, especially if you have that extra height. It's not that hard to change the escape wheel to one with fewer teeth to get the pendulum length you need.
    Willie X
     
  9. THTanner

    THTanner Registered User
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    It is a fun project, but getting out of hand. It is a lighted case with glass shelves and mirrors. Either way I go the glass shelves will need to be cut for the weights and pendulum. I think I have that figured. But, they also want me to put a mirror on the back of the face so that the front of the movement is reflected in the mirror at the back of the case. Sadly their clock went through a fire and the veneer was totally ruined and the glass broken during the fire fight. Their rebuild is a lot more modern than the original interior and they love the clock. Soooooo, we proceed.

     
  10. THTanner

    THTanner Registered User
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    This is a picture of the display case. The top glass shelf will become a seat board of sorts with holes and cut outs and a brass mounting U shaped plate for the movement with knurled through bolts and nuts. A rather sad change of life for a Lyre.
     

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  11. R. Croswell

    R. Croswell Registered User
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    Would be best if the cables were parallel. If you are going to modify the movement for a long pendulum, perhaps you can modify the bottom of both trains to drive from a single main wheel and spool?

    RC
     
  12. THTanner

    THTanner Registered User
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    Perhaps - but I am hoping to keep the movement as original as possible and modify the case to make it work and appear pleasing. Since the cables come off the outside of the drum if they go down instead of up to the top pulley, I am thinking I can use a little less weight since there should be less friction loss. The movement goes onto a mock up seat board later this week for testing some ideas. Right now I am planning to leave the pendulum and EW alone, but that might change.

     
  13. Tinker Dwight

    Tinker Dwight Registered User

    Oct 11, 2010
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    It is also possible that they do not understand the difference between
    the weights and the pendulum. We have seen that confusion quite
    often on the MB.
    If you go with the single weight, the Geneva stops should be enough.
    ( assuming it still has them ).
    Tinker Dwight
     
  14. THTanner

    THTanner Registered User
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    No Geneva stops on this weight movement. I suppose I could conjure one up, but I rather like the lever that tracks the cable instead.

     
  15. R. Croswell

    R. Croswell Registered User
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    Or simply attach (crimp on) some sort of brass sleeve or little ball that would contact the seat board when that spool is full. You may have issues with driving force when the weights are at the top and angle between the cables is large. If the cables were directed over pulleys under the seat board such that they were parallel you will have more constant power over the run cycle that will be a greater advantage than any thing gained from not having the friction of the pulleys.

    RC
     
  16. THTanner

    THTanner Registered User
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    I calculated - roughly - how low I would need to keep the single weight and it is just not a reasonable solution. So I am back to using two weights. I like the idea of a bead or decorative item attached to the strings to stop the weights on the underside of the seat board. Some delicate glass cutting and drilling and it should start going together.

     
  17. Jasons34

    Jasons34 Registered User

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    Just my opinion and remember I'm not at all good with figures or changing of a clock movement but looking at drawing won't work using a single pulley at the bottom since both trains will cause the cable to be pulled from different sides thus not allowing it to move. I don't have any program to draw up something but why not have a pulley for each side next to each other in the middle just below the seatboard. You can have hangers coming straight down from the seatboard so no issue of the pendulum hitting. So if you can picture this you'd have the cable from the left and right both going to the middle and running over the top of those pulleys and then straight down where they'd meet the weight. You'd gain a bit of overall length needed for an 8 day wind since the cables would be going horizontal for a bit instead of going vertical the entire time.
     
  18. THTanner

    THTanner Registered User
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    It actually does work pretty well, it is just cumbersome and gets in the way. The purpose of the pulley at the bottom is so that the single string can turn the pulley and keep the weight in the center as it descends when the time side unwinds and then to again remain in the middle as the strike side unwinds.

     
  19. Tinker Dwight

    Tinker Dwight Registered User

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    Too bad it wasn't a chain movement. One could set it up as a Huygens instead
    You not have to worry about winding because you only wind one side.
    Tinker Dwight
     
  20. dad1891

    dad1891 Registered User

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    Is the customer aware that the single weight design will place more force on the time and strike train when the weight is in the upper position, therefore wearing the movement more? Another downside is that the change in force will cause the movement to have timekeeping variations between the early and late part of the winding cycle, similar to a spring driven movement.
     
  21. Tinker Dwight

    Tinker Dwight Registered User

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    This can be avoided with a fixed pulley to bring the cables closer together.
    Tinker Dwight
     
  22. THTanner

    THTanner Registered User
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    Yes - I discussed this with them and we abandoned the single weight. And without the two pulleys per side in the usual case, I will probably be able to run it on 6 or 7 pound weights instead of the usual 8s. At this point two weights will be used and will fall pretty much straight down with perhaps a small angle to a roller near the bottom of the movement to keep the line away from the lower posts since the line will be coming off of the outside of the small drum.

    - - - Updated - - -

    Nice brass chains would look better too.


     
  23. RJSoftware

    RJSoftware Registered User

    Apr 15, 2005
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    Just to add my 2 cents. :)

    You can use extra cable pulleys and cable. You can arrange pulleys so the cable is partial hidden, perhaps routed to the back unseen. Then come back around again to view.

    You can double pulley a single line (pulley at top and bottom, cable wraps around twice) for example see Vienna. I think the rule is the more you pulley the system the more weight required. Don't know.

    You could also strip out the strike side and make it time only. Or talk them into a two weight system.

    RJ
     
  24. THTanner

    THTanner Registered User
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    Thanks RJ - I was able to talk them into a two weight system, but since it is glass and mirrors all around the cables and weights will have to be visible - but at least two weights is a lot simpler.

    btw I am about to wrap up the time stamp clock - how do the pictures and drawings look?

     
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