A spiral hairspring is molded from a resilient plastic material so that the several turns thereof are interconnected by a plurality of bridges to facilitate flowing the plastic material throughout the narrow confines of the mold passages. The interconnecting bridges are then cut from between the several turns to form the hairspring. Also, the hairspring may be molded integral with a shaft having a pinion gear thereon.
The invention relates mainly to a hairspring intended to equip the balance wheel of a mechanical timepiece. It is in the form of a spiraled rod (10) cut from an {001} single-crystal silicon plate. Its structure and its dimensions are calculated so as to minimize the thermal drift of the hairspring/balance-wheel assembly by means of the first and second thermal coefficients of its spring constant.
A hairspring and collet assembly for timepieces in which the collet has a base having an opening and a stud integral from the base in a direction parallel to the axis of the opening. The hairspring comprises an inner turn ending in a bend. The stud occupies a portion of the base extending between the opening and the periphery of the base. The non-deformed portion of the inner turn of the hairspring is secured to the stud and the bend extends freely away from the stud about the opening.
