400 day miniature Schatz has a worn-out jewel

Discussion in '400-Day & Atmos' started by kinsler33, Oct 13, 2019.

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  1. kinsler33

    kinsler33 Registered User

    Aug 17, 2014
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    Yes, I know that this belongs in torsion clocks, but I've decided to turn to a life of crime and ignore the rules.

    The Model 53's verge pivots are jeweled. On this clock, which has been utterly miserable to try to adjust, it turns out that the jewel on the removable plate (that is, a portion of the back plate) is worn out--oval, from side-to-side, and the side-shake is about three times the pivot diameter. The other (front) jewel seems fine and, as is typically the case with 400-day clocks, the rest of the pivots needed no attention.

    I did not know that jewels could do this. but it'll have to be replaced somehow. I think jewels just punch out like press-in bushings, but I'd need a replacement.

    Any advice? I could replace the jewel with a brass bushing, but the jewel would be more elegant.

    Anyway, I'm delighted that I've finally figured out why the clock is so feeble.

    Mark Kinsler
     
  2. gmorse

    gmorse Registered User
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    Jan 7, 2011
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    Hi Mark,

    Jewels don't usually wear like this, at least not if they're ruby or sapphire (corundum), but they do chip and crack if mishandled. Not all jewels are this hard substance, but could be anything lower down on the hardness scale, perhaps even quartz, (rock crystal). Whatever yours is made of, it's probably a friction fit as you suggest, (a picture would be helpful), and a replacement should be easy enough to source; you just need to know the hole and outside diameters.

    Seitz friction fit jewels come in very accurately graded dimensions, (both I/D and O/D), and to fit one back into a plate, the receiving hole has to be precisely the right size, just a whisker less than the jewel O/D, and perfectly cylindrical; no broaching! It also has to be pressed in perfectly straight, or there's a risk of cracking it. All this is best done with a jewelling press, but that's a pretty expensive tool to buy for one job if you don't already own it, or know a friend who has made the investment and knows how to use it.

    Regards,

    Graham
     
  3. kinsler33

    kinsler33 Registered User

    Aug 17, 2014
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    Thank you.

    I don't think I can take a useful photograph, but it kind of looks like the jewel, which is considerably thinner than the plate, is sort of staked in. For all I know it was glued.

    The hole in the jewel is pretty ragged, so I assume that it just chipped out. There's approximately no damage to the pivot itself. The other jewel seems to show some chipping as well.

    I've written to Chris Nimon at Horolovar to get his opinion, but what I'm inclined to do is knock out the precious jewels and put in brass bushings, which I'll likely have to make. The pivot diameter is around 0.54 mm, so a 0.6 mm KWM will fit, but the OD of that bushing is a bit too small for comfort.

    I'm inclined to agree with others that the jewels were just a selling point and unnecessary. Every other 400-day clock has done fine with brass pivot holes, and you never have to bush them because the clock is so slow.

    I suppose I ought to post this to torsion clocks, anyway.

    Mark Kinsler
     
  4. shutterbug

    shutterbug Moderator
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    Oct 19, 2005
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    I'll move it for you.
     
  5. kinsler33

    kinsler33 Registered User

    Aug 17, 2014
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    Ah, the power of monarchs.

    Thank you.

    M Kinsler
    No (0) Jewels
    Base metal bezel
    Titanium in back
     
  6. Chris Radek

    Chris Radek Registered User
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    Apr 13, 2014
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    There are Seitz jewels (up to) 56/260 and 58/300 available, and my standard Seitz jeweling set has 259 and 299 (the biggest) reamers. So if the hole can be cleaned up and still be under 3.00 mm, preferably under 2.60 mm, this is simple and I'd be happy to obtain and install the jewel for you. The technique I prefer to use is to ream in increasing size until the hole is just cleaned up, and then obtain the jewel with that outside diameter. Then the hole is as small as possible and it leaves material for future repairers in the unlikely event it needs to be done again.

    This all assumes the throat of the jeweling press is deep enough to get to the jewel. It sounds like it's in a removable smallish part so it should be fine.
     

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