OUT-OF-ROUND (HAIRSPRING DEFECT)

Out-of-round (hairspring defect) is a concentricity defect: it occurs when a wheel, a pinion or a Balance does not rotate in a perfectly concentric manner around its axis of rotation, but describes an eccentricity, a lateral “wobble”. The teeth or the Rim alternately moves away from and closer to the centre with each Lathe turn, which disrupts meshing, creates tight spots and impairs the regularity of the running; on a balance, an out-of-round (hairspring defect) unbalances the regulating organ. Concentricity is Testing — and an out-of-round (hairspring defect) is detected — by rotating the part between the points of a tool called a Figure-of-eight calliper, or on the staking tool, observing the movement of the periphery. The defect stems from a bent axis, imperfect fitting, or a shock. Its correction, through delicate straightening, requires method and precision. Out-of-round differs from Out-of-flat (hairspring defect), which affects rotational flatness rather than concentricity.