HELICAL

Something is described as Helical when it depicts or follows the shape of a helix, a geometric curve resulting from the combination, at constant pitch, of a rotation about an Axis and a translation along that same Axis. The Threading of a Screw offers the most familiar example: the Thread winds helically around the cylindrical body of the shaft, its pitch defining the axial advance obtained per complete Lathe. This geometry is also found in certain springs: a Helical spring, such as a compression or tension spring, winds in coils around an Axis, as opposed to the Hairspring (balance spring) flat design of the regulating organ, whose coils are coplanar and concentric. The so-called cylindrical Hairspring (balance spring) shares this same geometry: its terminal coils, raised out of the plane, breathe concentrically during changes in Amplitude, which significantly improves the Isochronism. Notably perfected by John Arnold at the end of the 18th century, it equipped many marine chronometers before being supplanted, in everyday watchmaking, by the flat Hairspring (balance spring) with an attached terminal curve. Understanding the helical shape remains useful for grasping the operation of screws, threaded rods, and various elastic components of the Movement.