Interchangeable parts

Wikipedia’s account describes the American system of watch manufacture as a set of methods taken from armory practice: interchangeable parts, a machine shop and quality control by gauge.²

Aaron Dennison took the idea from the Springfield Armory, where firearms were made from identical parts. From arms making the watch firm took a tight organisation, a central machine shop and a system based on models.^1, 2

Waltham made a model watch and a master set of gauges, and every part made afterwards was measured against the matching part of the model.¹

Its makers built specialised machines for each part and organised the work in a factory to speed production and cut costs. A simpler design helped: one mainspring in a going barrel, without fusee and chain, meant fewer parts.¹

The Pitkin brothers in Hartford had made watches with interchangeable parts between 1838 and 1845, before Waltham.^2, 5

According to Wikipedia’s account, parts were sorted by size, the closest-fitting going into the highest grades, and the tooling was enormous: Elgin used almost two drill bits for every watch it made.²

In practice parts were not always interchangeable: early machining left errors that had to be fitted by hand, and the machining improved over time.^2, 6

Watkins records that Jacques David, who studied the factories in 1876, used a strict definition, found jewels and pivots treated as unique, and saw that factories kept a record of every movement so a repairer could order an exact part by its number.⁶

Wikipedia’s account says labour remained the main cost, about 80 per cent of the cost of a watch in 1910 by one estimate, and that the know-how spread from Waltham to Elgin and on to dozens of other makers.²

To Switzerland

David told the Swiss to adopt American methods. Watkins says that the warning was heeded and the Swiss industry moved from the bench to the factory.⁶