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  1. #31
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    Default Re: Using glass for bushings (By: THTanner)

    Quote Originally Posted by THTanner View Post
    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.
    This is incorrect, read:

    https://www.scientificamerican.com/a...-glass-liquid/

    Phil

  2. #32

    Default Re: Using glass for bushings (By: THTanner)

    I agree, but it might be good for a temporary fix.

  3. #33
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    Default Re: Using glass for bushings (By: Phil Burman)

    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. "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 https://www.sciencedaily.com/releases/2007/08/070809130014.htm

    "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.
    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."

    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.

    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/publica...ics_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.

    Quote Originally Posted by Phil Burman View Post

  4. #34
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    Default Re: Using glass for bushings (By: THTanner)

    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

  5. #35
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    Default Re: Using glass for bushings (By: Tinker Dwight)

    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

  6. #36

    Default Re: Using glass for bushings (By: Phil Burman)

    Follow-up on my jeweling project.



    Final polishing the holes of the jewels


    The outcome, burnished into a chaton with bezel, and with #0-80 screws


    Mounted in the back cock

    The fully jeweled escapement, finally. It seems eager to run.

    More as it comes.
    Johnny
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