Since parts are interchangable, it is also possible to separate manufacture from assembly, and assembly may be carried out by semi-skilled labour on an assembly line - an example of the division of labour.
In order to eliminate hand tools, Whitney invented new machines to eliminate all skilled operations - introducing a kind of router to replace the chisel, for example.
History
In the early years of the USA, there was a severe shortage of skilled machinists. Whitney realised that by using a template, workers with little skill could not only operate machines, but also produce identical parts that were interchangeable.
Until then, under the English System invented during the Industrial Revolution, skilled machinists were required to produce parts from a design. But however skilled the machinist, parts were never identical, and each part had to be manufactured separately to fit its neighbours - almost always by one person who produced each completed item from start to finish.
Although there was still a requirement for the craftsmen to create prototypes of the design before production, they were no longer required in the actual manufacturing.
Whitney first used the sytem to manufacture muskets. Such was his reputation that the US government gave him a contract for 10,000 muskets, to be produced within two years, even though he had no factory or machines. It actually took eight years to deliver the order, as Whitney perfected and developed new techniques and machines, but he did go on to produce a further 15,000 muskets within the following two years.
European Origins
In fact, the concepts of the American System originated in France, and were first proposed for the production of guns by Honoré le Blanc in the mid 18th century. However the idea was resisted by the craftsmen, and was not developed on a significant scale.
It is thought that Whitney may first have heard of the idea from Thomas Jefferson, who at the time was the US ambassador in France.
The idea was first developed in Venice several hundred years ealier, where ships were produced using pre-manufactured parts, assembly lines, and mass production. The Venice Arsenal apparently produced nearly one ship every day, in what was effectively the world's first factory.Pre Industrial Revolution
Although the use of machines and templates was developed by le Blanc and Whitney, the idea of interchangeable parts and the separate assembly line was not new, though it was little used.