Jeweled Bushing question

Discussion in 'Clock Construction' started by brian fisher, Feb 26, 2020.

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  1. brian fisher

    brian fisher Registered User
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    Jan 20, 2017
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    i recently came across this web site: Ring Jewel Bearings | Quality Ring Jewels | Swiss Jewel

    this is a great resource for someone wanting to build a precision regulator i would say. they sell 7 different styles of bushings depending on the buyer's needs from .0881" all the way up to 1/4"! i noticed that 3 of them have the oil sink divot manufactured into the bushing? i always thought jeweled bushings weren't supposed to be oiled? what am i missing here?

    Brian
     
  2. Kevin W.

    Kevin W. Registered User
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    Some do oil them some dont. Varies i feel too, when to oil, when not to oil.
     
  3. brian fisher

    brian fisher Registered User
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    as an aside, i just called the company directly to get pricing. the jewels are about $3.00 each ranging up to about $11.00. the second largest bushing is about 65.00 and the largest .25" bush will cost about $75.00 each. other than the last two, i would say these are very inexpensive for what you are getting. if you consider the time involved, there is no way you could make them for this price.
     
  4. tok-tokkie

    tok-tokkie Registered User

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    I bought ring jewels and endstones from them. I made a variation of a gravity escape clock which I wrote up here on this thread. 30-Legged Gravity Escape Clock

    In my post #4 I wrote:
    I fitted the jewels some months ago & the clock has run beautifully with them. No longer is there gradual swing decay. I did oil the pivots. I later realised that I had failed to burnish the arbors where they run in the jewels. The arbors are through hardened and ground 2mm steel shafts. I used commercial plastic injection mould ejector pins as they are really hard and ground to size and straight. But burnishing them would have improved the surface finish.

    My jewels are listed as sapphire but they are glass clear. I had been expecting ruby red jewels. They can't be seen but I was disappointing by the color.
     
  5. Jim DuBois

    Jim DuBois Registered User
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    #5 Jim DuBois, Feb 27, 2020
    Last edited: Feb 27, 2020
    I can't offer any thoughts as to jewels used in watches, but jeweled regulators (clocks) call for a touch of oil to be used on the pivots. They also feature very hard and highly polished steel bearing surfaces running in the jewels. On some of the highest grade regulators, the jewels have end caps to limit dust contamination of the bearings, as well as dust covers over/around the movement plates.

    Personally, if I were to set forth to build a high-grade regulator I would build it with ceramic ball bearings running dry. Extensive testing of ball bearings, jeweled bearings, and regular bearings, with and without lubrication, show the dry ceramic bearings to be the most efficient solution and they do run with no lubrication. Less power required, less wear over time, no lube to fail, etc. But, they too need end caps and dust shields to maintain accuracy over time.

    From a very well detailed paper by Rex Swensen;
    "Surprisingly the results were the same for both diametric clearances. Again the oiled result came out slightly higher than the dry. According to a supplier of these jewels in the USA, a μ value of 0.15 is quoted, although I have seen values as low as .1 on other Internet sites. So the friction effects for jewelled bearings are not significantly lower than plain pivots.

    It should be noted that the accuracy of the plain pivot tests is based upon the counting of cycles and observing when the amplitude reaches the half amplitude mark. This is rather difficult to do on such a rapidly oscillating pendulum so the precision is about 1 in 16 cycles and the μ value is rounded to two significant digits.

    The big advantage of jewels appears to be in their wear resistance, and hence a much longer life than plain brass pivot holes. Also one may feel that they look more impressive in a clock and have popular “sales appeal”."

    "Comparison of Friction Results
    From these test results it would appear reasonable to assume a μ of 0.003 for the 2 mm ball races, if well soaked out in solvent. For plain pivots and jewelled pivots, a value of 0.15 - 0.18 is representative. This means that the plain pivot has about 60 times as much friction as the ball race. To achieve the same friction in a plain pivot it would have to have a diameter of 0.017 mm or 0.0007”.
    It should be noted that this analysis relates only to bearing friction, which is only one portion of the total friction losses in the train. Gear friction and escapement friction are probably much larger."

    214105_Howard3-1419359231.jpg 49303397_10156069956403105_7851980707134963712_n.jpg 49864960_10156069956448105_9139169550909046784_n.jpg 31356hj.jpg 31356hk.jpg
     
  6. gmorse

    gmorse Registered User
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    Hi Jim,

    In watch jewelling, (most commonly either the ruby or sapphire colour variants of corundum, aka aluminium oxide), the rotating and some sliding applications are indeed lubricated. Since its introduction in 1704, the jewel with a highly polished hole through it hasn't been bettered for friction reduction in the small sizes needed in watch movements, and the addition of endstones is vital for the proper working of balance wheels, as well as being most desirable for the faster moving escape and train wheels.

    Regards,

    Graham
     
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  7. John MacArthur

    John MacArthur Registered User
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    A couple of other advantages of a jewel over a plain brass pivot hole are: They retain the oil by surface tension instead of the oil spreading out over the brass plate. Also, they do not allow grains of dust to accumulate and embed into the bearing surface, creating the scoring action on the pivot.
    Johnny
     
  8. jhe.1973

    jhe.1973 Registered User
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    Hi Jim,

    Would you be able to identify for us the makers of the 5 movements your photos display?
     
  9. Jim DuBois

    Jim DuBois Registered User
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    Jim, the first movement pictured is a Howard 23 Astro Regulator. Here is a photo of the backside of that one. It is a long runner, how long I don't recall as that particular collection has some fair number of 30-60-90-120 day regulators. The next two photos are also Howards but I don't know the model of that timepiece, other than it lives in the same collection. The last two photos came out of the files I have and while I think it is a Howard I have no documentation on that one.

    But here is another fairly rare Howard, a 68 in this case. A couple of these ended up here as a prior owner had tossed the dust covers and thumbscrew retainers. One had conventional screws holding the side dust covers and the current owner wanted proper knurled thumbscrews made.

    howard 23 astro reg back.jpg howard astro regulator 68 back.jpg howard astro reg 68.jpg
     
  10. jhe.1973

    jhe.1973 Registered User
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    Thanks Jim for providing the details and the additional photos.

    You really did a great job on the thumbscrew in the middle shot ........................... it looks just like a thumb!

    Sorry about that, I just couldn't resist. :)
     
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