Using glass for bushings

Discussion in 'Clock Construction' started by karlmansson, Nov 8, 2016.

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  1. Jim DuBois

    Jim DuBois Registered User

    Jun 14, 2008
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    You can find a lot of perhaps relevant information at https://www.bocabearings.com/ball-bearings-in-clocks Rex Swensen has done a lot of work on the subject, so no need to reinvent the wheel....
     
  2. karlmansson

    karlmansson Registered User

    Apr 20, 2013
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    Thank you Jim!

    I was provided with the link to Boca Bearings earlier but did not manage to find the page you linked. Very informative! I Think I've learned all I need on the subject for now. Thank you to everyone who contributed!

    Best regards
    Karl
     
  3. jhe.1973

    jhe.1973 Donor

    Feb 12, 2011
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    Darn right there is interest!

    I had the opportunity/privilege of visiting Johhny in his shop last year and he was very helpful in explaining this jewel making process. But do you think I would remember all of the steps?

    screwball

    Nope not me. So please, pretty please keep us updated on your progress and I am so glad to hear that you have a "One of these days" write-up planned.

    I believe that there will be a LOT of interest in a thread that would showcase your craftsmanship and be inspiring to all as well.

    :thumb:
     
  4. John MacArthur

    John MacArthur Registered User

    Feb 13, 2007
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    Thanks for the kind words, Jim. I'm working on these between other stuff - they involve a lot of slow going. I *will* get them on board, though.

    Johnny
     
  5. Jim DuBois

    Jim DuBois Registered User

    Jun 14, 2008
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    Rhetorical question. Why have millions of watches been built with jewels and none built with glass bushings? That alone would give me pause, as glass is a lot cheaper than sapphire or diamond or other jewels used in watches. And capitalists will always be capitalists.....so if glass was a good substitute for jewels and it was much cheaper would it not have been used in millions of watches? I know little to nothing about watches but I do pay attention to the human condition if you will. It is my passing recollection that the jewels used in watches were selected for their ability to accept a fine high polish which then allows much reduced friction when fit properly to hard steel pivots. You all have covered this nicely in comments above. I am also aware that in some conditions glass can be very abrasive, even polished glass. There are of course other characteristics of jewels versus glass where jewels may fair best. In any event I would error on the side of caution and buy synthetic sapphire boules and stay away from glass. The cost of the synthetic products seems pretty reasonable to me. The cost of a jewel, no matter of what it is made is more in the time to make it than it is in the material.
     
  6. ccwk

    ccwk Registered User

    Jan 27, 2011
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    I will second that !
    To John and the others - Thanks for sharing your experiences
    Much appreciated Conwae
     
  7. karlmansson

    karlmansson Registered User

    Apr 20, 2013
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    Of course I realize that synthetic ruby would be superior to glass, considering how long it has been used and with what success. My question came from a place where I had trouble finding jewels of the size I required and thought that glass would be more easily worked and more easily obtainable than ruby boule. I'm interested in learing lapidary work as well so glass might be a good place to start out.

    For the application I asked about originally I think ball bearings are the way to go in any case. I do however appreciate the input from everyone and I am also looking forward to a more in depth look at making jewel bearings, when it come around!

    Best regards
    Karl
     
  8. Bill Ward

    Bill Ward Registered User

    Jan 8, 2003
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    I'm a bit dubious that a straight-line train would exhibit more problems with pivot location errors than another arrangement. Recall that the force applied to a pivot by a wheel tooth is (mainly) at right angles to the line of centers, though there is some pushing away of the pivot too (which varies with the tooth contact angle through tooth contact). And sure enough, what we see in worn plates is an oval hole whose long dimension is at about a 75-80 degree angle to the line of centers. Probably the worst arrangement, vis-a-vis pivot wear & cumulative position error for a train would be one where the wheels are at this this 75-80 degree angle to the line of centers; which is not always too different from what we usually have in existing clocks! Timepieces generally have train layouts that condense their dimensions to fit their cases.
    One reason that glass has not been used for bushings is that it's so brittle & breakable (compared to sapphire). But probably the real reason is economics: it's a lot easier to sell something for a high price if it's made with rare jewels, rather than broken bottles.
    But consider that brass bushings are considered sacrificial; it's a lot easier to re-bush than to repivot.
    Butter Bearings are really more a system for repair, than just simple bearings. They are sold in sets for specific repair jobs, e.g the Hermle floating balance movement. The pivots fit loosly into the bearing ID, which avoids precision alignment problems. The bearings are as easily set as brass bushings. This enables movementsw with plated pivots to be salvaged, and used, probably, another century- which is a lot more than they've lasted so far! And if you're worried about your rep long after you've been in the ground, just include an extra set or two in the case- that'll certainly earn you a prayer of thanks from some future clockmaker!
     
  9. Accutronica

    Accutronica Registered User

    Nov 21, 2016
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    Very interesting thread. I can't wait to see more.
     
  10. THTanner

    THTanner Registered User

    Jul 3, 2016
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    Glass is actually a very viscous liquid. Even a small piece of glass will change shape over time under constant pressure. Large windows get thicker at the bottom versus the top under the force of gravity. I don't know how long it takes in terms of size and pressure, but if you are wanting to use glass to make a long lasting bearing you are probably not going to be happy after a few years.
     
  11. Phil Burman

    Phil Burman Registered User

    Mar 8, 2014
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    This is incorrect, read:

    https://www.scientificamerican.com/article/fact-fiction-glass-liquid/

    Phil:)
     
  12. Accutronica

    Accutronica Registered User

    Nov 21, 2016
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    I agree, but it might be good for a temporary fix.
     
  13. THTanner

    THTanner Registered User

    Jul 3, 2016
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    That is a discussion about "Super Cooled Liquids" - and states "Like liquids, these disorganized solids can flow, albeit very slowly. "

    Newer research is showing more clearly when and why glass molecules do move and what constrains these motions. "[FONT=&quot]The movement of the glass molecules slows as temperature cools, but they never lock into crystal patterns. Instead, they jumble up and gradually become glassier, or more viscous." from [/FONT]https://www.sciencedaily.com/releases/2007/08/070809130014.htm

    [FONT=&quot]"The problem with glass-forming materials – which include plastics, alloys and ceramics in addition to everyday “glass” – is that there is no obvious transformation. On cooling we cannot definitively say yet that glass has become a solid." This study takes if further and discusses why some areas in a piece of glass appear more solid than others and why some are less viscous. [/FONT][FONT=&quot]
    [/FONT]
    http://www.iflscience.com/chemistry/glass-solid-or-liquid/

    Under stress it gets a lot more complicated.


    "You may be surprised to learn that glass is an elastic material on the atomic level. This means that under stress, glass will deform due to the nature of its atomic bonding structure." "The elastic nature of glass is described by its elastic moduli. These moduli tell you a lot about how much a glass will deform under stress and in what direction it will deform. They are defined by the relationships between different directional elements of stress and strain. Three important and commonly used elastic moduli are Young’s modulus, Poisson’s ratio, and the Shear modulus."

    [FONT=&quot]And there are very different kinds of glass with different properties that affect how much they deform under stress. The addition of silica, soda lime silicates and borosilicates changes the properties such as flexibility and sheer resistance. But glass does "flow" under stress at the molecular level, albeit very slowly and sometimes returns close to its previous shape when the stress is relieved.

    [/FONT]
    This study talks about the changes in the chemical bonds that allow the molecules to flow under pressure and how it occurs. https://www.researchgate.net/public...e_And_Stress_by_Molecular_Dynamics_Simulation

    It is a poorly understood process with lots of variables. But current research shows that glass molecules do flow under stress at normal temperatures.

     
  14. Tinker Dwight

    Tinker Dwight Registered User

    Oct 11, 2010
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    Regardless, glass is too easily scratched. It is not particularly hard.
    Anyone that has had the misfortune to have the rubber come of a
    wiper blade. In just a few minutes, there are scratches in the glass.
    I doubt it would work well as a bushing.
    Tinker Dwight
     
  15. Phil Burman

    Phil Burman Registered User

    Mar 8, 2014
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    TH, in the link I gave Robert Brill, an antique glass researcher at the Corning Museum of Glass in Corning, N.Y. says:

    "Furthermore, cathedral glass should not flow because it is hundreds of degrees below its glass-transition temperature, Ediger adds. A mathematical model shows it would take longer than the universe has existed for room temperature cathedral glass to rearrange itself to appear melted."

    The reference you gave relates to glass behaviour under stresses in the GPa range, that's 145,000 psi. Most anything will flow under that kind of stress, however I doubt a clock bearing will see those kind of numbers under normal usage.

    Phil:)
     
  16. John MacArthur

    John MacArthur Registered User

    Feb 13, 2007
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    Follow-up on my jeweling project.

    [​IMG]
    [​IMG]
    Final polishing the holes of the jewels

    [​IMG]
    The outcome, burnished into a chaton with bezel, and with #0-80 screws

    [​IMG]
    Mounted in the back cock
    [​IMG]
    The fully jeweled escapement, finally. It seems eager to run.

    More as it comes.
    Johnny
     

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