Beat Error - Now what
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  1. #1
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    Beat Error - Now what

    So next up the repair of a Bulova movement.

    I finally broke down and bought a timing machine.

    It shows the watch as - 19 seconds with a beat error of 2.8ms. (hopefully picture uploaded)

    But can someone explain to me fundamentally what that means?

    This is my guess -----

    The 2.8ms is not a problem w/ the going train as that would just slow down the movement entirely... .

    It must be a problem w/ the escape or balance wheel????

    It is probably not a problem w/ the arbor or the escape wheel as that would affect the movement unilaterally ????

    I am guessing it is most likely a problem w/ the pallet jewels or the guard fork???

    I just don't understand beat error.

    Can someone explain to a novice?

    At the end of the day my question is how do I diagnose and repair this problem?

    I am having a real hard time understanding and interpreting beat error.

    -TL
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  2. #2
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    Re: Beat Error - Now what

    The balance swings in both directions, a movement is "in beat" if both swings are equal in length. 2.8 ms means the swing in one direction is 2.8 ms longer than the the other direction. The total time for both swings can be correct and the watch can be regulated, but positional variation may be off quite a bit. Also, being "out of beat" may keep the movement from self starting.

    To correct this, the terminal end of the balance spring must be moved relative to the neutral position of the pallet fork.
    familiaritas parit contemptum; raritate admiratione wins.- Lucius Apuleius
    est necessry, accurate ad secundo? - Lysander magna
    iustum est horologium - Obscurus Genius

  3. #3
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    Re: Beat Error - Now what

    Just to continue with your question, to repair this problem could mean one of two things: Either you have a movable stud carrier on your balance cock, or you don't. If you do, you carefully move the stud to bring the watch into beat. If there is a fixed stud, it becomes complicated. The hairspring will have to be made perfectly flat, perfectly round, (you'd be surprised how often this is necessary, even in 'new' watches.) and perfectly in the centre of the regulating pins. An observation will be made with a high power loupe to see where the regulating pin is when the pallet fork is in the middle of its banks. What you're looking for, is how far off and to which side the pin is when the balance is at rest. Then the balance bridge is unscrewed and the balance removed from the watch. The balance wheel with hairspring is then removed from the balance cock. Using the specialty collet-turning tool (I use the Bergeon set) you then carefully rotate the collet to bring the whole assembly in line with your observations. Then you reassemble the balance, check the beat error, and chances are it will still be off. You do this as many times as necessary to get the watch into beat. I try and get 'good' old watches down to at least .5 ms, but sometimes this is difficult, and it depends on the watch. Wear and tear in old watches make for large positional errors, because most watches are never serviced regularly, so you may see the amplitude fluctuate as well as the rate in vertical positions, which will affect the beat error analysis. If the watch's amplitude drops, the beat error will drop also. Ideally, you want to adjust the beat error with the watch running flat, fully wound, and demagnetized, with the hairspring properly adjusted beforehand.

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  5. #4
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    Re: Beat Error - Now what

    So the movement in question is a Bulova 10csc

    used Bulova 10csc automatic watch movement for parts .. | eBay believe the stud is fixed.

    so what I want to do is:

    1) remove the hair spring from the stud and the collet to examine for round and flat.
    2) adjust collet
    3) reattach hair spring
    4) measure
    4) rinse and repeat?

    fundamentally what has caused the watch to be out of beat?

    The watch is unadjusted so did it always have this error or is it that the hair spring is losing elasticity?

    -TL

  6. #5
    Member Outta Time's Avatar
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    Re: Beat Error - Now what

    If that movt has been rattling around outside a case for any length of time, it's a miracle it isn't damaged in other ways. It would most likely need a complete service. Then, freshly lubricated and clean, it should be examined on a timing machine. While the balance is still in the watch, you can see what it is doing, whether it is flat or out of round. Also you can observe what is happening between the regulating pins, is the the spring bouncing between one and the other, or is it leaning against one or the other? Other than that, your order of operations is correct. In old watches, shocks can throw the balance out by distorting the hairspring ever so slightly. (or severely, as I have seen in even some very expensive new watches) Springs eventually get tired, not only from half a century or more of running, but also removal and manipulation, corrosion, etc. Usually a well cared for watch can run for much longer. Watches would sometimes be stamped 'unadjusted' to avoid certain tariffs upon being imported, so it may be meaningless and usually is. All the little bumps and bangs of everyday life do have an impact on the tiny mechanism.

  7. #6
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    Re: Beat Error - Now what

    Quote Originally Posted by Tomslow View Post
    1) remove the hair spring from the stud and the collet to examine for round and flat.
    -TL
    No need to remove the balance spring assembly (spring, collet and stud) from the balance wheel, if that is what you are suggesting here. As OT suggested, look at the flatness and concentricity of the spring while it's in the watch. To adjust the beat error by rotating the collet, I remove the balance cock/bridge with the balance attached, place it on a balance tack, and carefully feed the collet rotating tool through the upper spring coils, and slightly rotate the collet. Not a job for the inexperienced, but it's not terribly difficult to do once you get some practice.

    If the balance wheel is unusually heavy and the spring is fairly weak I will sometimes remove the balance from the balance cock/bridge completely and make the adjustment - that might be a better approach when you are starting out so you don't have to feed the collet tool through the spring. I will also do this on some watches where the coils are very small and tight, and it's difficult to get the tool fed in from above. In any case, treat the spring with care and don't bounce the wheel around while it's hanging.

    Be prepared to chase the beat error around a bit, and also make very small adjustments, and keep track of them so you always know which way you rotated the collet on the last move. There are some days when it seems you will chase it like crazy to get that last .2 or .3 out, and other days I'll make one adjustment and it hits zero.

    Hope this helps.

    Cheers, Al

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    Re: Beat Error - Now what

    A good helpful thread

  9. #8
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    Re: Beat Error - Now what

    The way I usually do it is separate the balance with spring from the balance cock, and place the balance back in the watch, engaging the pallet fork with the impulsion pin, or roller pin. Carefully holding the rim of the balance with tweezers, rotate it in a tiny arc, and observe the movement of the pallet fork, it should move too. When it is right in the middle, or appears to be, carefully lower the balance cock back down a bit and see where the stud hole is in relation to where the stud is hanging right now. That will tell you which direction and how much to rotate the collet. This is a trial and error method, and gets a bit fiddly. I haven't tried Al's method, but I will do so next time I have a dangly balance that I can sneak into from the top without removing it from the cock, which is quite a lot of the vintage ones. The trick here is not to distort the hairspring while doing any of this. The old Blue ones get magnetized very easily, so always make sure your tools, tweezers, etc. are de-magged.
    Also keep in mind the pivots of the balance are very very tiny (.11 mm, for ex.) and break easily. Pressure must be avoided on the staff if it is sitting in the watch, and not allowed to flop sideways either while sitting in the lower jewel. While re-assembling the balance into the watch, it is critical to be sure it is free at all times while the cock is screwed carefully down. I give it a little swing or twist while it is in the movement holder, and watch it swing while I tighten the screw. I do this a couple times til I get the balance cock screwed down, and if at any time the little wheel looks like it is binding, do not exert any pressure, and see why it is not moving. The last thing you want to hear is that horrible little sound that means the pivot broke.
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