Jewel's on escapement's teeth?

Thread: Jewel's on escapement's teeth?

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  1. #1
    SCD
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    Jewel's on escapement's teeth?

    Oh goofy...the thread title shouldn't have an apostrophe! Anyway...

    I'm new to this and learning quickly the rudiments of mechanical watch movements...so I have a rookie question. I think I understand the point of jewels, that they're harder and wear much more slowly. So I gather this is the reason for jewel pallets on a pallet fork. By the same logic then isn't there a necessity for jewels on the teeth of the escapement wheel? Why does steel suffice there?
    Last edited by SCD; November 14th, 2009 at 04:08.

  2. #2
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    Re: Jewel's on escapement's teeth?

    Quote Originally Posted by SCD View Post
    isn't there a necessity for jewels on the teeth of the escapement wheel? Why does steel suffice there?
    Simple math - the standard escape wheel has 15 teeth as contact points vs. 2 pallet jewels as contact points on the Swiss lever. That means 7.5 times more concussion from contact so the jewels are necessary. On the high beat 36,000 bph movements the escape wheel has 21 teeth.

    Here's a link to just about all you need to know about the basics of a watch:

    http://www.watchtalkforums.info/foru...ad.php?t=22496

    It's like "Watches for Dummies" in cliff notes form. It was surely written by a dummy.

  3. #3
    SCD
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    Re: Jewel's on escapement's teeth?

    Makes sense...thanks.

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    Re: Jewel's on escapement's teeth?

    I'll offer another reason: friction. The coefficient of friction between sapphire and high-carbon steel, lubricated or unlubricated, is among the lowest there is. Even lower than the CoF for sapphire-on-sapphire. Lower friction = lower power loss in the train.

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    Re: Jewel's on escapement's teeth?

    Quote Originally Posted by tee530 View Post
    I'll offer another reason: friction. The coefficient of friction between sapphire and high-carbon steel, lubricated or unlubricated, is among the lowest there is. Even lower than the CoF for sapphire-on-sapphire. Lower friction = lower power loss in the train.
    Now that's good stuff.

  7. #6
    SCD
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    Re: Jewel's on escapement's teeth?

    Quote Originally Posted by tee530 View Post
    I'll offer another reason: friction. The coefficient of friction between sapphire and high-carbon steel, lubricated or unlubricated, is among the lowest there is. Even lower than the CoF for sapphire-on-sapphire. Lower friction = lower power loss in the train.
    Aha!

  8. #7
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    Re: Jewel's on escapement's teeth?

    Quote Originally Posted by tee530 View Post
    I'll offer another reason: friction. The coefficient of friction between sapphire and high-carbon steel, lubricated or unlubricated, is among the lowest there is. Even lower than the CoF for sapphire-on-sapphire. Lower friction = lower power loss in the train.
    Ditto, since lever escapements function by friction. Ruby jewels are also very brittle, and thus having jewels constantly smacking into one another might not be ideal (complete hypothesis made up by me, who knows, maybe that isn't a problem), where as steel is much less brittle. This is why watch manufacturers have switched from steel bearings to ceramic coated steel bearings as a superior solution to a jewelled pivot in automatic winding mechanisms.

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