Broken strike hammer spring on Korean Sehwa 31-day movement

Discussion in 'Clock Repair' started by Elliott Wolin, Jun 1, 2020.

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  1. Elliott Wolin

    Elliott Wolin Registered User
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    Got one of these on Craigslist, mostly working but the strike hammer spring snapped off and I don't see it anywhere. You can see the notch in the hammer assembly where the spring fits. Note that the snail/cannon cock is removed in this picture, the spring was held by the cock screw (it was like a leaf spring, not a coil spring, similar to the one at top left pressing against part of the rack assembly).

    Seems like I could just attach a coil spring to the hammer assembly just about anywhere and anchor it in various places. But I wonder if someone has a tried-and-true fix for this.

    20200601_162441.jpg 20200601_162447.jpg 20200601_162458.jpg 20200601_162540.jpg
     
  2. roughbarked

    roughbarked Registered User

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    To fit a coil spring you are going to have to tie those mainsprings off, let the tension off onto the ties and pull the plates apart. A lot of dangerous work for the love of a coil spring.

    Try using a pair of shears to cut up a soft drink can and make one of these. I like the SOLO cans myself. You'll need to punch a hole for the screw or rivet and you'll need to get the shape and bends right.

    P6026639.JPG P6026640.JPG
     
  3. Elliott Wolin

    Elliott Wolin Registered User
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    Soda can spring is a good idea, I'll have to find a soda can (we don't drink soda) or something similar. Important thing is the metal can't lose it springiness over time.

    As for the coil spring, I wasn't planning on taking the movement apart, with those monster springs, I thought I could figure something out.
     
  4. roughbarked

    roughbarked Registered User

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    #4 roughbarked, Jun 1, 2020
    Last edited: Jun 1, 2020
    The coil spring needs to be mounted on the strike hammer axis, thus needs to be slid onto the shaft which requires the plates to come apart.
    The spring is only there as a recoil bounce damper. The risk of loss of tension through fatigue is low.

    One doesn't need to be a soft drink buyer. Hundreds of millions of cans are tossed on the roadside in your state every year.
     
  5. Elliott Wolin

    Elliott Wolin Registered User
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    Temporary solution, for testing.

    20200601_191241.jpg
     
  6. Elliott Wolin

    Elliott Wolin Registered User
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    I looked carefully and I see no evidence of a coil spring on the strike hammer, only the flat spring you say is only for rebound. No broken bits or remnants of a coil anywhere.

    Is it possible at some point the manufacturer realized the rebound spring (possibly beefed up) was all that was needed and stopped including a coil spring on the strike hammer?

    Note that the movement is in pretty good shape and seems to keep good time. I'd like to avoid taking it apart if possible. Too bad they don't make 20-year service life rubber bands.:)
     
  7. roughbarked

    roughbarked Registered User

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    These Korean clocks. They were all manufactured with the same spring. They never had a coil spring.
    The American clocks did.
     
  8. shutterbug

    shutterbug Moderator
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    The clock isn't of great value, so your temporary fix will work if you substitute a coiled spring from the local hardware for the rubber band. If you can hook the spring to a washer it would let the winding square turn inside it without winding it up as you wind the clock.
     
  9. David S

    David S Registered User
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    #9 David S, Jun 2, 2020
    Last edited: Jun 2, 2020
    Here is a pic of the missing spring.
    Movement with spring keepers.jpg

    David

    Opps, missed the pic in post #2.
     
  10. Elliott Wolin

    Elliott Wolin Registered User
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    Thanks for all the help. I'll try cutting up an aluminum can to make a replacement spring. If that doesn't work I'll try a coil spring and washer (good idea, the washer), unless the washer interferes with something, in which case I'll perform some minor surgery to install a post or something for the spring to attach to.

    My main goal is to not have to take the movement apart, it's running fine now and there doesn't seem to be much pivot wear. About the only thing I see is some sticking in the mainsprings, I'm hoping a little Slick 50 spray on the outside of the springs will work its way in and eliminate the sticking. Or maybe this is just wishful thinking...maybe I should just take the plunge and take the movement apart. It's those massive springs, though...
     
  11. David S

    David S Registered User
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    I don't think an aluminum can will make a good spring. Part of an old mainspring or a piece of steel shipping banding will work.

    David
     
  12. roughbarked

    roughbarked Registered User

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    These springs aren't steel originally.
     
  13. Elliott Wolin

    Elliott Wolin Registered User
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    Played with a bit of mainspring, the only one I have, but even cut really narrow it's too stiff. There's a lot of swing to the hammer so the spring has to be really light and springy, not stiff.

    Can mainsprings be tempered somehow to make them less stiff? I only have a propane torch and all it could do is turn a bit of mainspring red and quite brittle. I thought heating metal and cooling slowly tends to soften it, I thought rapid quenching is what makes metal stiff and brittle. I guess I know little about this.

    If Al can material doesn't work, what's a good alternative? Brass shim stock?
     
  14. roughbarked

    roughbarked Registered User

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    #14 roughbarked, Jun 2, 2020
    Last edited: Jun 2, 2020
    I haven't tested the original spring material but it looks like phosphor bronze perhaps. I don't believe it is though as phosphor bronze hairsprings can get brittle and break easily. This material is so soft it is easily damaged by the slightest of rough handling.
    Drink cans particularly those wearing the SOLO brand are easily a stronger spring and more readily available. Not that I've tried them all but I definitely wouldn't use a coke can or alternatively do try a coke can as I may be overestimating the unusability here. Try a few brands and stamp on them. If they compress easily then maybe they aren't strong enough but if they are a little more difficult to compress then they will be strong enough. I've got dozen or so of these springs but the postage would be a prohibitive cost when all sorts of slightly springy metal can be found laying around in the street. The object of the spring is to push against the slot ever so slightly. It isn't intended to be pulled on by a rubber band.
    If you were going to use a mainspring, I'd use a watch mainspring of the weaker strengths available.

    If you can get any material in cut able lengths or sheets that can also be used for suspension springs this will do the job.
     
  15. David S

    David S Registered User
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    If you have a dollar store near by, you can get a retractable usb cable, key chain, pet leash or anything else that is small and retractable and take the return spring out of it. Even a piece of feeler gauge.

    David
     
  16. shutterbug

    shutterbug Moderator
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    Feeler gauge is inexpensive and easy to find, and you can select the best "fit". Good idea.
     
  17. Uhralt

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    Thin brass shim stock should work. If not springy enough, you can harden it by hammering.

    Uhralt
     
  18. R. Croswell

    R. Croswell Registered User

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    I think an aluminum soda can "spring" would be too easily bent to last. There is no reason the spring has to be flat. A piece of thin music wire or steel guitar string should also work and I believe would be more durable and perhaps also easier to shape.

    RC
     
  19. roughbarked

    roughbarked Registered User

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    I can assure al who doubt it that;
    a) all soft drink cans are not equal
    b) all of them will have more resistance than the original spring
     
  20. kinsler33

    kinsler33 Registered User

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    For delicate springs do not ignore the virtues of suspension spring stock, or suspension springs themselves. That's what I use when I need a bit of very thin steel.

    But in this situation I would favor a spring made of brass wire, somewhat on the order of the helper springs used in count-wheel clocks, or somewhat heavier. Make a loop in one end so you can screw it to the plate and bend the rest of the wire so that it contacts the hammer without interfering with anything else.

    For what it's worth I have not had any bad experiences with 30-day springs. They go into a C-clip nicely enough, or you can use a worm-gear hose clamp or a wrapping of heavy wire (the latter is the easiest to remove after the spring is back in the clock.) Just be careful and professional. I've had worse luck with 8-day springs, which are amazingly easy to underestimate.
     
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  21. roughbarked

    roughbarked Registered User

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    I don't know why I keep having to repeat it though. The original spring on these clocks is so soft that if you happen to bump it, it will need readjustment to make it work again.
    Yes, if any replacement were better then use it. However, it may be too strong.
     
  22. shutterbug

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    I guess it depends on whether its a return spring or a bumper as Rough described. If the latter, his solution would work fine.
     
  23. roughbarked

    roughbarked Registered User

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    It is only to dampen the bounce of the hammer.
     
  24. Elliott Wolin

    Elliott Wolin Registered User
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    The hammer will fall towards the gong by gravity alone, but not with much oomph. I suspect it wouldn't make much of a gong. The striking mechanism lifts the hammer against the spring a fair distance and then let's go. The hammer heads towards the gong with a bit more oomph this time, and the spring additionally controls hammer rebound.

    So it does both to my understanding. But it really is a pretty weak spring. I'll have to find an Al can someplace, perhaps from one of the neighbors, along a road, or left in a picnic area. I have lots of wood bits here and there from woodworking, but hardly any metal or wire...I'd better start collecting some (my wife didn't hear that!).
     
  25. kinsler33

    kinsler33 Registered User

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    Um, are we to understand that you, a repairer of clocks and presumably other items, do not collect junk? That you can walk through a parking lot without retrieving the occasional nut, bolt, or sheet-metal screw? That you don't save wire or steel strapping? That you do not carry a magnet to check for brass? That you do not possess a collection of exceedingly-deceased quartz movements, cut-off bits of brass or steel rod, and enough mainsprings to equip the Tsar of Russia?
     
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  26. Elliott Wolin

    Elliott Wolin Registered User
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    While my wife and kids will testify that I collect precious items that definitely will be used one day related to woodworking, car repair, plumbing, home repair, electrical stuff, and sailboats and kayaks, they would be lying if they said I did the same for metal parts other than nuts and bolts.

    But now that I've been invited into the inner circle of watch and clock repairers (thank you, kinsler33), and been given the special instructions concerning collection of definitely-will-be-used-one-day metal parts, I will faithfully proceed as instructed. Condolences to my family...

    Now, what about the secret handshake?
     
  27. roughbarked

    roughbarked Registered User

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    Your wife will want to leave unless she's very understanding and accomodating. Has happened to all the clock/watchmakers I know.
    You don't want her knowing the secret handshake.
     
  28. Elliott Wolin

    Elliott Wolin Registered User
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    Indeed!
     
  29. roughbarked

    roughbarked Registered User

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    It is true though. The shop owner said to me, "You watchmakers are all the same. Every tiny bit of rubbish always has other uses nobody else can envisage". That's because over the past 66 years, he'd known five different watchmakers in his daily life.
     
  30. JimmyOz

    JimmyOz Registered User

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    Every time I have a clean out nothing ends up going, it is more about remembering what I do have and where it is. Which reminds me, the inside of the quarts movements have a flat spring that may do the job of the spring you need, however a soda can shouldo work as Roughbarket said, however never tried it but now I CAN!
     
  31. roughbarked

    roughbarked Registered User

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    Yes you can. :)

    I merely move the stuff around and if any real rubbish falls out, then it goes to the bin. The big problem is the amount of time I have to spend on my knees sorting spilled parts. My knees are getting too old for that.
     
  32. roughbarked

    roughbarked Registered User

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    If you are talking about the battery contacts, they are too strong.
     
  33. shutterbug

    shutterbug Moderator
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    I tell my family that I do it for them. The more stuff I have at the end, the more they'll collect at the estate sale! I'm not sure they are buying it though. What we repairmen and collectors know and never reveal is that whoever has the biggest pile at the end of the game WINS! I think I have a pretty fair chance :D
     
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  34. TooManyClocks

    TooManyClocks Registered User
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    I think I’ll try telling that one to my wife!:)

    Something tells me I wouldn’t get very far though...oh well...:oops:

    John
     
  35. roughbarked

    roughbarked Registered User

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    Photos or we'll never believe it.
     
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  36. roughbarked

    roughbarked Registered User

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    This material is easily more durable than the original spring material.

    P6066678.JPG
     

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