Fusee (horology)

A snail is at mechanical watches with spring plant a cone-shaped roll with a spiral groove on the pulling means ( string, string, etc.), which transmits the driving force from the spring works on clock movement is wound.

Function

The screw is axially parallel mounted between the spring mechanism and the going train. It is from her grown gear from the direct drive of the going train. The effluent Federnwerk the screw rotates by winds the traction elements of her off and on its outer cylinder (constant diameter RH). The unwinding takes place initially by the small diameter of the screw (RS). Then the Abwickeldurchmesser increases so that the slowly decreasing output torque from the mainspring barrel ( MF) at an approximately constant drive torque for the screw (MS ) is translated to throughout nearly the same to drive the clock movement.

The flow rate of the spring mechanism ( ωF ) increases proportionally with increasing winding radius of the screw ( rS ), because the input power (P) should remain constant in order to keep the error on the speed of the rotating mechanism ( ωS ) is small.

• P = ω · M; M = r · Z; Z = traction device power
• P = ωF · RH · Z = ωS · rS · Z
• ωF = ωS · rS · Z / ( rh · Z)

Constant are ωS and RH.

• ωF ~ rS.

History

The spindle watches were in principle less accurate than the subsequent clocks with swinging regulator. Watches with spring mechanism were due to the highly variable during execution spring force particularly at a disadvantage.

The compensating solution by means of a set screw between already existed at the beginning of the 15th century, first with a gut string, and later with a chain. Some newer table clocks instead of the chain also a flexible steel band is fitted.

Efforts to calculate the optimum cross-section of the screw ( the first attempts of Pierre de Varignon, 1702 ) failed, only a few decades ago the problem was solved positively. Before trying the watchmakers to find the cheapest way empirically.

For pocket watches, the chain links were extremely fine. At 12 cm chain length went up to 800 members.