Maintaining and Repairing Mechanical Watches by Mark W Wiles

Author:Mark W Wiles
Language: eng
Format: epub
ISBN: 9781785001567
Publisher: Crowood

The two most common types of balance in modern and antique watches are the bi-metallic balance, and the plain/annular balance.

Bi-metallic Balance

Fig. 159: Bi-metallic balances. Image 1: (A) Brass rim of the balance wheel. (B) Steel inner rim of the balance wheel. Image 2: (A) Stud (fixing point of the spring). (B) Cover coil spring. (C) index pins. A watch with an over-coiled balance spring is best left to more experienced watch repairers, as these are very easily damaged.

A bi-metallic balance is where the rim of the balance has been made of two strips of metal (one brass and one steel).This outer rim is also cut through either side of the balance’s centre crossing, so that the balance now has two semi-circular arms. The theory behind the balance wheel is that brass has a bigger coefficient of expansion than that of steel, so as the two bands of metal are joined together, this causes a natural bending effect as the two metals expand and contract at different rates. In cold weather, this would cause the balance rim to bend outwards, cancelling out the natural shrinking effect of the balance wheel. The opposite occurs in hot weather, as the balance rim bends inwards, compensating for the expansion of the whole balance.

Plain Balance or Annular Balance

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