Snail (clock)

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mechanical clockwork with worm and chain between spring mechanism (left) and movement (right rear); at the thick end of the worm is the drive gear for the movement

In mechanical watches with a spring mechanism, a worm is a conical roller with a spiral groove on which a traction device (string, chain, etc.), which transfers the drive force from the spring mechanism to the movement, is wound.

function

The worm is mounted axially parallel between the spring mechanism and the walking mechanism . It is the direct drive of the movement from its attached gear. The running spring mechanism turns the worm by unwinding the traction mechanism from it and winding it onto its outer cylinder (constant diameter r F ). The unwinding takes place initially from the small diameter of the screw (r S ). Then the unwinding diameter increases, so that the slowly decreasing output torque from the barrel (M F ) is translated to an almost constant drive torque for the worm (M S ) in order to drive the walking gear almost equally.

The running speed of the spring mechanism (ω F ) increases proportionally as the winding radius of the worm (r S ) increases, because the drive power (P) should remain constant in order to keep the error on the running speed of the slewing mechanism (ω S ) small.

  • P = ω * M; M = r * Z; Z = traction force
  • P = ω F r F Z = ω S r S Z
  • ω F = ω S r S Z / (r F Z)

Ω S and r F are constant .

  • ω F ~ r S .

history

The spindle clocks were in principle less precise than the following clocks with oscillating rate regulator . Clocks with a spring mechanism were at a particular disadvantage because of the highly variable spring force when running .

The compensating solution with the help of an intermediate worm already existed at the beginning of the 15th century, initially with a gut string , later with a chain . Some newer table clocks have a flexible steel band instead of the chain.

Efforts to calculate the optimal cross-section of the snail (first attempts by Pierre de Varignon , 1702) failed; only a few decades ago the problem could be resolved conclusively. Before that, watchmakers tried to empirically find the cheapest shape .

With pocket watches , the chain links were extremely fine. There were up to 800 links on a 12 cm chain.

literature

  • Richard Reutebuch: The watchmaker: A textbook f. every watchmaker, .... ; Wilhelm Kempter Verlag, Ulm (Donau) 1951; P. 162f
  • Zdeněk Martínek and Jaroslav Řehoř: Mechanical watches. VEB Verlag Technik Berlin, 1988; ISBN 3-341-00022-4 ; P. 66f
  • Alfred Holiński: Jacob Zech and a Royal Fusee Clock. In: The Connoisseur. 152, 1963, pp. 183-187.

See also

Web links

Commons : Snail  - collection of images, videos and audio files

Individual evidence

  1. ↑ Lukas Stolberg: Lexicon of the pocket watch ; Carinthia Verlag; Klagenfurt 1995; ISBN 3-85378-423-2 ; P. 201