Original Mainspring Dimensions -HAC W77 Movement

Discussion in 'Clock Repair' started by Chrisb, Aug 25, 2018.

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  1. Chrisb

    Chrisb Registered User

    Oct 9, 2015
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    Engineer
    Fourways, Gauteng, South Africa.
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    Hi All, Could anyone please advise what the original dimensions were for the mainsprings fitted to these movements in the Going and Strike trains at the time of manufacture ? The movement is marked as follows:

    W77 over
    "Crossed arrows", ie 'HAC', bottom left hand side of rear plate.

    187/35 over
    83, top left hand side of the rear plate,

    345, (date code ?), top right hand side of rear plate.

    Movement is Time and strike, only.

    Many thanks in advance,
     
  2. Willie X

    Willie X Registered User

    Feb 9, 2008
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    Well, I can give you some tips to go on.
    Width is a given, 1mm less than the space available. Strength is the big question mark. On German clocks the strike spring is often thicker than the time spring by 1 to 3 thou. Once the strength/thickness is chosen, the optimum length can be calculated.

    Do you have any parts of the old springs, this would help a lot. At least you would have some reference. If not, a good guess (or starting point) would be 15 thou for the time and 17 thou for the strike. The calculation will yield the correct lengths for the respective barrells. Assuming the barrels are the same size the time spring will probably be about 10" longer that the thicker strike spring. Willie X
     
  3. Chrisb

    Chrisb Registered User

    Oct 9, 2015
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    1
    3
    Male
    Engineer
    Fourways, Gauteng, South Africa.
    Country Flag:
    Hi Willie X,

    Many thanks' for the response, much appreciated.

    Unfortunately, there where no springs with the Movement to work from. I recall that what is usually found in the USA movements on the strike side is: 0.45mm x 17mm x the length needed as calculated. I would think the 0.45mm / 18 thou would be too strong for the Going train ?

    Kind Regards,
     
  4. Bruce Alexander

    Bruce Alexander Registered User
    Sponsor NAWCC Brass Member

    Feb 22, 2010
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