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The Encyclopedia of Horology

Component record · Plates & finishing

Pivots

Verified

The finely turned, reduced-diameter ends of an arbor that run in bearings, jewels or bushings.

What it does

Provide the low-friction rotating support points for every wheel, pinion and lever arbor in the movement.

How it works

A pivot is turned down to a precise, small diameter and polished to a very fine finish, since surface imperfections directly increase friction and wear against its bearing (jewel or plain hole).

The balance staff's pivots are the most critical in the movement: they must be extremely fine, perfectly round, and well polished, since even minor imperfections here measurably affect amplitude, rate and shock resistance, which is why shock-protection systems (see Jewels) specifically cushion the balance pivots.

A bent or broken pivot is one of the most common serious faults in watch and clock repair, usually requiring the arbor to be re-pivoted (a fine new pivot turned and fitted) by a skilled watchmaker rather than simple replacement of an off-the-shelf part.

Evolution

Pivot-turning precision has steadily improved with lathe and tooling technology, and hardened, polished pivots running in synthetic jewel bearings became standard through the 20th century for reduced wear.

Known variations

  • Plain steel pivot running in a brass bearing
  • Pivot running in a jewel bearing
  • Shock-protected pivot (balance staff) running in a spring-mounted jewel setting

Identification for collectors

  • A wheel that wobbles, binds, or runs unevenly often indicates a bent or worn pivot
  • Pivots are inspected under magnification for straightness, polish and correct diameter during service

Common failure modes

  • Bending or breaking, especially from impact (very common on the balance staff)
  • Wear from insufficient lubrication or worn bearings
  • Rust pitting from moisture ingress

Photographs

Mechanical appliances, mechanical movements and novelties of construction; a complete work and a continuation, as a second volume, of the author's book entitled "Mechanical movements, powers and (14761412126)
Mechanical appliances, mechanical movements and novelties of construction; a complete work and a continuation, as a second volume, of the author's book entitled "Mechanical movements, powers and (14761412126) — Internet Archive Book Images, No restrictions. Wikimedia Commons file page
Mechanical appliances, mechanical movements and novelties of construction; a complete work and a continuation, as a second volume, of the author's book entitled "Mechanical movements, powers and (14766816715)
Mechanical appliances, mechanical movements and novelties of construction; a complete work and a continuation, as a second volume, of the author's book entitled "Mechanical movements, powers and (14766816715) — Internet Archive Book Images, No restrictions. Wikimedia Commons file page

Photographs are illustrative examples of the type, not necessarily the exact object described. Verify details against the source file page.

Sources & references

  1. de Carle, D., Practical Watch Repairing

Where sources disagree, the disagreement is stated rather than resolved silently.