Pendulums
  • Probably a daft question - but what would cause a clock to slow down? I've noticed that this summer I've had to move my pendulum bob down (to increase the frequency) a bit to keep my Septimus on time. it's more than a cm lower than it was last summer.

    Obviously, things like heat, dust, etc will cause a clock to change it's characteristics and increase friction - but I wouldn't have thought that would cause the clock to slow. Stop, certainly - a greater drive weight might be needed to overcome frictional forces - but not to require a change in pendulum length. What could be causing this?

    Dave F
  • One of the things that is very often forgotten about mechanical clocks is actually how much work they do in the course of a day. The Septimus uses a seconds pendulum which means it takes one second for each swing, or rather 2 seconds to return to the starting point, as each swing takes a second that means it is swinging at the rate of 86400 times a day.
    So imagine what affect even a small environmental change would have, so lets say at the end of the day the clock was off by 2 minutes ( 120 seconds)

    120/86400=0,0013888

    Which basically means for each swing there is a plus/minus of 0,001388 of a second, which in anybodies book is an infinitesimally small amount of time, but times it by the amount of swings in a day and you already have a noticeable inaccuracy.

    Obviously things like humidity and temperature can cause any pendulum to shorten or lengthen, but one major culprit that hardly ever gets mentioned is air pressure.
    Fluctuations can be so sever that from one day to the next you can have literally tons more resting on your shoulders, but we are geared up for such changes a clock less so.

    As a pendulum swings through air then a slight change in density will affect the frequency.

    As I am never tired of saying, the clocks we have built are absolutely accurate it is just that sometimes the world we live in is not :-)



  • I too have been noticing that my Septimus, that I've just finished on 26th January 2015, is lagging behind by 2-3 minutes every 24 hours. I tried adjusting the pendulum bob in the last 4 days but its not making any difference.
    Any other alternative?
  • Presuming that you have picked up on the fact that with a compound pendulum, as with the Septimus, the lower adjusting bob moves down to speed the Septimus up and not upwards as with a "normal" pendulum.
    You have 2 choices, either you reduce the weight of the upper bob or increase the weight of the lower bob, but before you pull out your hacksaw just tape a small bolt or similar to the lower pendulum rod so that you increase it´s weight, you should notice the Septimus speeds up.

    Dave
  • While waiting for the Sextus to arrive and reading the manual, you have us putting weight (26E) in the pendula "bob bed".

    1. What is the purpose of this added weight? Better swinging force?

    2. Is this a case where more (weight) might be better? (I have some brass discs that would up the weight quite easily.) Less effected by barometric pressure variances?

    3. Does the weight in these pendulums affect the required amount of drive force weight?

    4. Your reply above to Ashok above suggests: "... reduce the weight of the upper bob". Would it be best to delay closing up the bobs (27E) till the clock has been run in and adjusted?

    5. A completed 27E would be upsetting if access was required during "tune in". Perhaps leaving the backside of the bobs off would be wise or would this recommendation be considered an unusual adjustment step ?
    Thanks!
  • 1. The period of a pendulum is a function of its weight and length, removing the washers would mean longer pendula or a shorter period.

    2. The supplied washers are of the correct weight, so no need to replace.

    3. The heavier an object the more force it requires to move it, so there is a direct correlation between mass and force. However the Sextus kit works as is, there is no need to change anything.

    4. The advice given to Ashok applies to the Septimus pendulum and has little/no relevance to the Sextus Pendula.

    5. Please take a closer look at page 48 of the instructions.
  • Dave / others, My Sextus pendula "free" swing for a little over 60 seconds! Nice!
    The clock system also passes the "blow test". Will move the minute hand +30 minutes around the clock face on a good "birthday" blow.

    When I add the weight, after + - 25 seconds of running, the left paddle will hang onto the escapement gear. I believe this stoppage is from a continually degrading pendulum swing arch.

    Questions are:
    1. What or how is the weight drive force transferred to maintain the pendulums' swing?
    2. What can I do to improve the pendulum swing once weight has been added to the system and stop this frustration!???
  • Okay- After much closer scrutiny, I see that the escapement wheel gently pulls the left paddle up just a bit during its (2948 gm weighted) rotation before the paddel counter balances away from the gear tooth.
    Still at a loss for the solution. Thx.
  • Welcome to the wonderful world of "fiddling " with a brand new clock :). If the drive force seems to be enough to supply the push and pull of the pendulum than there may be a simple quick fix. Sounds like you have a "sticky" left pallet, to which I've read about before. Try this simple diagnostic - take blue tack or painters tape and apply it to the bottom of the left pallet to see if it helps to disengage it from the escape. If it still doesn't have enough force, remove the tape and add a small washer with tape to the same area. Also, make sure that the pallets are property aligned to the escape. Misaligned pallets will "bury" into an escape and potentially stick. Give it a go as none of these steps would be detrimental to the clock, but may provide a clue.....
  • Hey thanks for chiming in so fast Chris with your suggestions - again!
    I will try the tape idea as I have already polished up the surfaces of both the escapement teeth and the pallet "cups" about as good as I'm capable. I was playing with thin sheet lead pieces taped to the lower half of the pallet, but have since added a little graphite to all the surfaces and it flops very freely (and reliably) while in hand with the added weight back on the work bench.
    My thinking has been if Dave didn't need it, I need to find and remove the why mine appears to need it.
    I added 85 more gm. to the weight so it is now at 3033 gm total.
    http://www.towerhobbies.com/help/convcalcs.html

    If I wasn't so technologically challenged in getting the videos off my phone and on to You Tube, those would be there for your visual scrutiny!
    Another challenge to conquer this week!
  • Good luck!
  • The blue tape on the right paddle has seemed to get the clock running 10-15minutes. I actually think there was a time when both paddles were engaged to the escapement gear, frustrating the push momentum and causing a very short run time. Its a bit hard to watch them both at the same time but I do believe this paddle lock scenario has been overcome.

    Adding the tape is nagging me to sand a polish those paddles a bit more so it can be removed.
    But hey, the joy in this 15 minute run time is enough to carry my motivation for now!
  • It also could be binding more than the pallets. Check for friction between the cogs. This may also be the problem making the pallets look as if they aren't functioning properly.
  • A couple of things to bear in mind, firstly the Grasshopper, and I stress this is in no way a technical or approved term, is a "pulled" escapement. Which basically means when a pallet engages it "pulls" the pendulum as opposed to a deadbeat which "pushes", if the drive force is not enough it can happen that the pendulum moves with more energy than the escapement wheel, which will cause the pallet to disengage before the other one has engaged, and worse case scenario is that your escapement wheel free runs and mutates into a high speed circular saw blade.

    Secondly what can also happen is that the pallet counter weight can be too heavy and cause the pallet to disengage just by its sheer weight, this quite often happens just before the other pallet engages causing the escapement wheel to lap against the pallet.

    But I have had quite a bit of feedback about the left pallet being too "lazy" and not disengaging correctly, or disengaging but not hitting the stop and re-engaging, and I must admit it is on a bit of a hair trigger, so I have now slightly increased the diameter of the counter weight, which should solve the problem that some have been having.

    @Mark
    Clock making is a bit like riding a bike, you can read all the books you want and get all the advice in the world, but until you put your arse on that saddle and fall off a few times you are never going to be able to ride a bike.
    Observe with an open eye and a open mind and approach all problems with thought and calm, and I promise you one thing, when your Sextus runs as it should you will know a lot more about clocks than before :-)

  • Mark, I absolutely have to agree with Dave on the "ride and fall" statement. My first clock was an utter disaster (Not purchased from here I must add) and has become "still life" on my workbench. But I learned......a lot. You soon get the feel for the tolerances needed and accuracy required, along with the satisfaction of sharpening your problem solving skills. Since then I have progressed midway in my second, more complex clock build and she already runs :). You will get it, and along with it the total satisfaction of seeing that wonderful mechanism run on the wall ;)
  • Let me first qualify that I am enjoying this build a lot. I actually thought building it would have been harder.
    As for my current challenges, my Uncle summed it up best with saying: Through adversity fond memories are made!
    Also it always a joy to get a chime in from the designer extraordinaire!
    This weekend is devoted to mastering the challenges of video in an posting on You Tube so my severe rookie articulation can be assisted with visuals!
    I'm confident this project will see the light of the family room!
  • Okay 1/23/16 - here is my first You Tube "test for tenacity". I believe only a Sextus builder can relate 99.75%. Hey, if you see any odd reactions in need of attention, please do speak up.
    Movement stopped at 12 minutes or so, so this is only 7+ minutes of my lefty & rightey pallets bumping the spring stops. That's it.

    I'm now ready to disassemble (last time?) and complete the finishing!
    https://youtu.be/DnmkJFtSOLQ
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