ETA escape teeth chamfered

Discussion in 'Wrist Watches' started by xpatUSA, Jan 31, 2008.

  1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.
  1. xpatUSA

    xpatUSA Registered User

    Apr 25, 2006
    344
    2
    0
    Country Flag:
    Region Flag:
    Hi All,

    I've often noticed the chamfer on ETA 27xx and 28xx escape wheels. It's on the dial side of the wheel teeth and reduces the area on the impulse faces by about 60%

    Here's a pic . .

    http://www.tedcossins.com/nawcc/macro/ETA_esc512.jpg

    Is this a common manufacturer's practice? Does anyone know the reason?

    cheers,

    Ted
     
    Berry Greene likes this.
  2. John Runciman

    John Runciman Registered User
    NAWCC Fellow NAWCC Member

    Aug 13, 2003
    256
    7
    18
    Seattle, WA
    Country Flag:
    Region Flag:
    By decreasing the contact area of escape wheel you reduce the amount of friction. Reducing friction in the escapement will decrease the influence it has timekeeping.
     
    Berry Greene likes this.
  3. xpatUSA

    xpatUSA Registered User

    Apr 25, 2006
    344
    2
    0
    Country Flag:
    Region Flag:
    Thanks John - that's exactly the part I didn't understand because what I've read about friction says the force of friction is independent of contact area (all other things being equal).

    If I read what you said correctly, this is not the case for a sapphire/steel interface?

    cheers,

    Ted


     
    Berry Greene likes this.
  4. John Runciman

    John Runciman Registered User
    NAWCC Fellow NAWCC Member

    Aug 13, 2003
    256
    7
    18
    Seattle, WA
    Country Flag:
    Region Flag:
    So I googled "friction is independent of contact area" I found a couple links I'm giving one below.

    So I looked at their examples and all I can tell you is in watches they've gone to considerable length to reduce contact area in a variety of locations I assume for friction reasons. Then we toss in lubrication how does that affect things. Amusingly the first link I found which I'm not giving was friction for dummies. The amusing aspect was the comment made that as you reduce the contact area at some point in time you start digging in and in friction will increase considerably more. But typically in the watch where contact has been reduced is steel on Sapphire. Occasionally on older pocket watches you will see curved stones on the pallet fork which would reduce the contact. another example of reduced contact is plate jewels versus balance jewels. The balance jewel has considerable less contact on the balance staff I believe for a reduction of friction. So yes according to Wikipedia according to the rules on friction none of this seems to make sense at all but yet the watch companies have gone to considerable lengths to do it. Then of course we throw in lubrication and that changes everything.

    Friction - Wikipedia
     

Share This Page