American System of Manufacturing - Interchangeable Parts

Interchangeable Parts

The American System involved semi-skilled labor using machine tools and jigs to make standardized, identical, interchangeable parts, manufactured to a tolerance, which could be assembled with a minimum of time and skill, requiring little to no fitting. The system is also known as armory practice because of the history of its development by the United States Department of War in the Springfield and Harpers Ferry armories (and their inside and outside gun-making contractors). The name "American system" came not from any aspect of the system that is unique to the American national character, but simply from the fact that for a time in the 19th century it was strongly associated with the American companies who first successfully implemented it, and how their methods contrasted (at that time) with those of British and continental European companies. Within a few decades, manufacturing technology had evolved further, and the ideas behind the "American" system were in use worldwide.

Since the parts are interchangeable, it is also possible to separate manufacture from assembly, and assembly may be carried out by semi-skilled labor on an assembly line - an example of the division of labor. The system typically involves substituting specialized machinery to replace hand tools.

Interchangeability of parts was finally achieved by combining a number of innovations and improvements in machining operations and machine tools, which were developed primarily for making textile machinery. These innovations included the invention of new machine tools and jigs (in both cases, for guiding the cutting tool), fixtures for holding the work in the proper position, and blocks and gauges to check the accuracy of the finished parts.