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Thread: A slight inconvenience...

  1. #1
    Craftsman
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    A slight inconvenience...



    I have been watching these cracks in the acrylic crystal grow and develop over the last month or two. They started off as a small cluster of half a dozen localised, tiny fractures which have slowly grown and joined up until they are two large cracks. Before I dive in to replacement of the crystal I am trying to find out more about the failure mechanism to reduce the repeat of recurrence.

    I am not sure what has caused them but I am fairly sure there wasn't an impact as there are no gouges or other signs of damage on the surface. I also think I would have noticed a knock hard enough to crack the crystal. To my untrained eye, at the beginning, they looked like tiny stress fractures deep within the acrylic. Is this a common occurrence in acrylic crystals

    My vague theory is that the original crystal had been replaced but, in the absence of the correct size, a slightly oversized one was squeezed in. This set up of stresses within the crystal which were increased, perhaps with the case expanding in the heat of summer. Is it possible for an acrylic crystal to fail like this or am I over thinking it and it's a case of shoddy workmanship?

    Moving onto the subject of a replacement, I know that Eddie no longer has spares and that the diameter is 32.4mm. I am not sure of my terminology but I am guessing the style on the PRS-29A is a box crystal. Are all acrylic box crystals all created equal or am I better off buying one from a particular source? Do I need to buying anything else like gaskets etc?

    I expect that I'll end up sending it to one of the forum's resident watchmakers as this is one of my favourites and I would be peeved if I ballsed it up but any answers to the above questions will be gratefully received and noted for future reference as I am keen in to improve my tinkering skills.

  2. #2
    Master .olli.'s Avatar
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    It looks like an acrylic crystal with tension ring. I have not handled / inspected this particular model from Eddie’s, but I would have thought a Sternkreuz domed crystal ATC type with chrome tension ring would do the job (available from CousinsUK or HS Walsh for best price). They do not require any gasket, the tension ring “pushes” the acrylic against the case creating a watertight seal.
    Happy to help if you get stuck.

  3. #3
    Craftsman
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    Thanks for information Olli, I might well take you up on your offer too.

    Anyway, thought I'd add a photo showing the profile of the crystal. It does look more domed than box.



    Tapatapatapatapatalk

  4. #4
    Master .olli.'s Avatar
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    Yes looks like a dome crystal.
    For info here is the profile of the Sternkreuz ATC, as fitted to a G10 I had on the bench today


  5. #5
    Grand Master
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    Agree with olli, Sternkreuz ATC should do the job, but whoever fixes it needs the watch on the bench to check what will fit best, sometimes it’s not straightforward.

    As for the cause of failure, I’ve seen it happen before and I can’t explain it. Crystals are always under some tension when fitted so I’d discount this. I’ve seen it on old crystals when they get a scratch, within a few hours the crystal goes almost crazy-paved in appearance. On a much younger watch I suspect its the quality of the acrylic that’s questionable.

    I’ve never had problems with Sternkreutz, they’re made in Europe and the quality is excellent.
    Last edited by walkerwek1958; 7th October 2019 at 21:02.

  6. #6
    Grand Master
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    I will look in my box, I might have a spare crystal.

  7. #7
    Craftsman
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    Thank you all for the further advice.

    It looks like the failure was one of those things that occasionally happens which is a relief, or perhaps I did knock and didn't realise.

    Thanks again.

    Tapatapatapatapatalk

  8. #8
    Craftsman
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    Well it has been a few months but beneath the Christmas tree for me this year was a crystal press. So, after a bit of practice on an old watch I thought I'd get stuck in:



    Well that was reasonably easy.



    Comparing the original, on the right, with the newer Sternkreutz on the left the profiles are different. For the sharp eyed amongst you yes, the replacement is 0.1mm wider than the original (as measured with my vernier anyway) (32.4mm compared with 32.3mm). The same tool measured the opening at 32.2mm.



    Would the difference in sizes explain why it isn't sat square? I did remove and replace a couple,of times and this is the best I achieved. When I place my next order from Cousins I'll add the two other sizes to it and see if I can make it better.



    Still it is currently good enough to use:



    Except that it isn't. Despite my best efforts (clearly not good enough) I managed to balls up removing the stem as it goes in but doesn't engage the keyless works. A full strip and reassembly is required. B@/#"!+s.

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