Is this a dust cover or an anti-magnetic shield?

Thread: Is this a dust cover or an anti-magnetic shield?

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  1. #1
    Member David.Boettcher's Avatar
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    Is this a dust cover or an anti-magnetic shield?

    I have been researching watch cases manufactured by the Swiss company Taubert & Fils, successors to the watch making company of François Borgel. They made a line of patented watch cases with screw back that are distinguished by having 10 flats (decagonal) for gripping with a key or wrench to unscrew them.

    Some of these cases also have an inner cover, as shown in the picture of a West End Watch Co. "Sowar Prima" below. They are beautifully engineered - they fit very snugly onto a spigot in the case back inside the groove that carries the lead gasket. The little raised area is not an accidental dent, it indicates the presence of a small slot on the edge of the cover for a finger nail or screwdriver to remove it. I think the little nub in the centre of the inner cover is for the case back to hold it in place when screwed on, although there is no corresponding mark on the case back. Not all Taubert decagonal cases have these inner covers. They are sometimes described as a dust cover, sometimes as an anti-magnetic movement cover. I am puzzled by this cover - here are my thoughts on these two possibilities.
    • Dust cover: The screw back, precision made and tightening down onto a lead washer, forms a very effective seal, so why would an inner dust cover be required? But if it was needed for some reason, wouldn't all such cases be fitted with it?
    • Anti-magnetic cover: I have in the back of my mind that an anti-magnetic shield needs to be made of a ferromagnetic material which can divert the lines of magnetic flux around the object contained within it. This is different to a Faraday cage which can be made of any conducting material, but does not protect contained items from static magnetic fields. I thought at first that the inner cover in the picture was nickel from its colour and general appearance, which would do the job because nickel is one of the few metals apart from iron that is ferromagnetic. But it is definitely not ferromagnetic - a magnet shows no sign of being attracted to it whatsover. The stainless steel case back is actually more magnetic than the inner cover!

    Does anyone know what this inner cover is actually there for? I could well be wrong about the anti-magnetic shield business, as this does appear to be the most likely reason for the inner cover. It just looks and feels more like an anti-magnetic shield than a dust cover, and you could have knocked me over with a feather when the magnet just slipped off it.

    Thanks for sharing your knowledge, or for any thoughts or suggestions!

    Regards - David


  2. #2
    Member Erik_H's Avatar
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    Re: Is this a dust cover or an anti-magnetic shield?

    I thought (as you did) an antimagnetic cover needs to be ferromagnetic. Soft iron that is. Sorry for being clueless, I would like to have an answer to this as well.
    Erik_H
    Member NAWCC Chapter 149

  3. #3
    Member radger's Avatar
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    Re: Is this a dust cover or an anti-magnetic shield?

    Do these inner covers act as a movement spacer ring and keep the movement from
    being loose in its case? If so then I'd say that these so called dust covers are simply an upmarket
    movement spacer ring, if not then I don't know the reason for this inner cover.

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  5. #4
    Vint. Forum Co-Moderator Mirius's Avatar
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    Re: Is this a dust cover or an anti-magnetic shield?

    Those ones, if it is the same as mine, fit snugly into a movement ring which holds the movement tightly into the case. So not a movement ring. Yet I've seen very similar covers on other watches - such as sixties Roamers. I've speculated as to whether these in fact are copies of the Taubert waterproof system, especially given that nipple. OK the Roamers use the standard slotted back not a decagonal, yet is it coincidence that Roamer abandoned it's proprietary waterproof case and replaced with this much more 'standard' and cheaper(?) one, presumably when the Taubert patents ran out?

    Those Roamer ones do sometimes act as a movement ring and they have a slot cut out to allow the stem through, so they hardly add to the waterproofing? Yet how can they be a dust cover? That said, those movements are nearly always very clean even if rarely if ever serviced.

    Anti-magnetic? Perhaps?


  6. #5
    Member radger's Avatar
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    Re: Is this a dust cover or an anti-magnetic shield?

    Quote Originally Posted by Mirius View Post
    Those ones, if it is the same as mine, fit snugly into a movement ring which holds the movement tightly into the case.
    Is this cover compressing the movement ring and holding it and the movement snugly in place when the back is tightened
    to it? If so then perhaps that is its function.

  7. #6
    Member AbslomRob's Avatar
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    Re: Is this a dust cover or an anti-magnetic shield?

    I see those a lot on some US a-11 spec military watches, but not all; I've always understood it to be a dust guard of some sort.
    My growing collection of "affordable" vintages: http://www.abslomrob.com

  8. #7
    Member David.Boettcher's Avatar
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    Re: Is this a dust cover or an anti-magnetic shield?

    Quote Originally Posted by radger View Post
    Is this cover compressing the movement ring and holding it and the movement snugly in place when the back is tightened to it? If so then perhaps that is its function.
    Thanks Mirius and Radger, spot on as usual.

    I don't normally do this because I am a bit nervous with the old screwdrivers and tweezers, but I took the movement out of the West End watch. The movement is held in a carrier ring which is a good snug fit into the case, but not a friction fit. Once the stem is out, the movement and carrier ring drop out of the case, then you remove the case screws and the movement pushes out from the carrier ring. As Radger says the inner cover holds the carrier ring in place in the case, and as Mirius says there is a slot in the ring for the stem. The cover is stamped CS(I) for Civil Service (India) so this watch has seen the tropics but, like Mirius says, the movement is bright and clean so the case has done a pretty good job over the years.

    The top picture shows the movement and carrier ring, the bottom picture the carrier ring with the cover in place.

    So Sotheby's were wrong when they described it as an " a-magnetic movement cover" on this Taubert cased Patek Philippe reference 1463 chronograph: Sotheby's - Catalogue

    My only problem now is what to call the flipping thing . . . dust cover, inner cover, cuvette?

    On second thoughts, that's not my only problem: the real question is why did they make it like that? It does remind me of the original Borgel screw in case where the movement is carried in a threaded ring, held into it by two screws just like this one.

    Thanks for everyone's input!

    Regards - David



  9. #8
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    Re: Is this a dust cover or an anti-magnetic shield?

    Hi there,

    to make a long message short: These caps do nothing but keeping the movement in place.

    It is simply hard to believe that any manufacturer is crazy enough to use a dust cap (with wide gap for the stem) in a waterproof case. But I thought it could be possible that any of them believed that such a thin cap can shortcut more than earth magnetism. So I tested over a couple of years whether any of these caps were made of iron. But I found none, and meanwhile I'm convinced the the idiot density in watch industry is not higher than in the non-watchmaking fraction of menkind.

    Regards, Roland Ranfft

  10. #9
    Vint. Forum Co-Moderator Mirius's Avatar
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    Re: Is this a dust cover or an anti-magnetic shield?

    In the case of mine it isn't a slot - only on the later Roamer 'copies' who didn't use a movement ring



    In my case not being a slot didn't help as the cork seal failed and there is extensive rust in the keyless works


  11. #10
    Member trim's Avatar
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    Re: Is this a dust cover or an anti-magnetic shield?

    I will just add to Mirius's explanation - the mid 1970s Roamer watches evolved to a plastic version of this set up. In my opinion that 100% rules out the anti magnetic theory. Also, by this stage, antimagnetic HS etc were old hat.

    BTW, Roamer used this alongside the Roamer Patent waterproof case, on their cheaper ranges - it did not replace it.

    Earlier watches certainly had a similar setup in dustproof watches. I agree with Roland - what use is this in a waterproof case? I doubt any sensible manufacturer would waste the few cents needed to make this if it had no real function. I believe it is simply for superior location. The dimple in the back is acted on by the case back. No need to use annoying and easily lost screws that come loose in service - it is likely cheaper to make such a sprung cover than the screws - as it can be cheaply stamped out.

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