Fitting new balance

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  • #50236
    jhargrove77
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    • Topics Started: 6
    • Total Posts: 19

    Hey gang,
    I’m working on a Bulova pocket watch 17AE. It had a mangled hairspring when I opened it up. I tried straightening it but wasn’t 100% satisfied with result so I bought a new balance assembly that came with a new mounted hairspring. Problem is, I think one of the pivots may be too large for the jewel hole. Haven’t tested this theory completely yet but if it is, what is my best option? If if pull the new hairspring off and put on the old balance, how does that affect the vibration? If I use the new assembly, do I polish pivot to fit hole or try to enlarge jewel hole?

    jim

    #65301
    drichards
    Participant
    • Topics Started: 3
    • Total Posts: 35

    Hello Jim,

    I’m not certain if this applies to the movements that Bulova used but many of the older American companies made their balance staffs with pivot purchase options for O.S. – oversized pivots.
    Whether this applies to the 17AE I don’t know right now. I’m visiting my son and away from my Best-fit reference book to check. In any case I often run across the need to polish the pivot down a little to make it fit the jewel. I advise this course of action over the others you mentioned.
    Opening a jewel hole and then polishing it can be a of a chore and changes any future staff replacement dimension requirements and, really wouldn’t be necessary anyway since a jewel with a slightly larger diameter hole can substituted instead.
    Changing the hairspring from one balance to another can sometimes work okay but no guarantee since the hairspring should be vibrated to each individual balance.
    I usually just use a Jacot tool to grind and polish it down. Normally just takes a minute. Other option is a simple pivot polisher or on the lathe.

    All the best Jim! Dean

    #65302
    jhargrove77
    Participant
    • Topics Started: 6
    • Total Posts: 19

    Thanks Dean,
    Your answer was pretty much inline with my thoughts. I was a little apprehensive about polishing a pivot this small but it is what it is. I guess I get try something new.

    Best wishes
    jim

    #65303
    jhargrove77
    Participant
    • Topics Started: 6
    • Total Posts: 19

    Ok gang. I’m back again. Verified new balance staff is a little too long. If I leave the balance cock screw out and slightly lift it up, the watch will run. I’m thinking of shimming the balance cock. what’s the best method to do that? what material? Is it good practice?

    jim

    #65304
    randy
    Participant
    • Topics Started: 39
    • Total Posts: 594

    Hey Jim.
    Thought I would jump in on this.
    While it’s not the preferred method, you can shim the balance. If you take this route, make sure that you get really good amplitude, which will indicate that you aren’t rubbing the end of the staff against one of the capstones too tight. Check this in Dial -up and Dial- down positions.
    I would suggest using some timing washers under the cock screw. or on either side of the screw hole. Please don’t use a “method” that some watchbreakers did, where they used a graver to dig up metal under the cock in order to raise it. That’s heresy !!!

    Now..I get the feeling that you aren’t comfortable putting the balance on a lathe or Jacot to reduce the length. I can feel your pain. :D
    Have you thought of using a hand-held pivot polishing tool ? If you aren’t familiar with them..they have cups on each end that you can place the staff pivot into.
    Perhaps ?? This would be aggressive enough to allow you to remove enough material in a controlled manner..perhaps…..

    Best of luck

    Randy

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jhargrove77Fitting new balance