Interchangeable parts

Interchangeable parts are parts (components) that are, for practical purposes, identical. They are made to specifications that ensure that they are so nearly identical that they will fit into any assembly of the same type. One such part can freely replace another, without any custom fitting, such as filing. This interchangeability allows easy assembly of new devices, and easier repair of existing devices, while minimizing both the time and skill required of the person doing the assembly or repair.

The concept of interchangeability was crucial to the introduction of the assembly line at the beginning of the 20th century, and has become an important element of some modern manufacturing but is missing from other important industries.

Interchangeability of parts was achieved by combining a number of innovations and improvements in machining operations and the invention of several machine tools, such as the slide rest lathe, screw-cutting lathe, turret lathe, milling machine and metal planer. Additional innovations included jigs for guiding the machine tools, fixtures for holding the workpiece in the proper position, and blocks and gauges to check the accuracy of the finished parts.[1] Electrification allowed individual machine tools to be powered by electric motors, eliminating line shaft drives from steam engines or water power and allowing higher speeds, making modern large scale manufacturing possible.[2] Modern machine tools often have numerical control (NC) which evolved into CNC (computerized numeric control) when microprocessors became available.

Methods for industrial production of interchangeable parts in the United States were first developed in the nineteenth century. The term American system of manufacturing was sometimes applied to them at the time, in distinction from earlier methods. Within a few decades such methods were in use in various countries, so American system is now a term of historical reference rather than current industrial nomenclature.

First use

Evidence of the use of interchangeable parts can be traced back over two thousand years to Carthage in the First Punic War. Carthaginian ships had standardized, interchangeable parts that even came with assembly instructions akin to "tab a into slot b" marked on them.[3]

In East Asia during the Warring States period and later the Qin Dynasty, bronze crossbow triggers and locking mechanisms were mass-produced and made to be interchangeable.

Origins of the modern concept

In the late 18th century, French General Jean-Baptiste Vaquette de Gribeauval promoted standardized weapons in what became known as the Système Gribeauval after it was issued as a royal order in 1765. (Its focus at the time was artillery more than muskets or handguns.) One of the accomplishments of the system was that solid cast cannons were bored to precise tolerances, which allowed the walls to be thinner than cannons poured with hollow cores. However, because cores were often off center, the wall thickness determined the size of the bore. Standardized boring allowed cannons to be shorter without sacrificing accuracy and range because of the tighter fit of the shells. It also allowed standardization of the shells.[1]

Before the 18th century, devices such as guns were made one at a time by gunsmiths in a unique manner. If one single component of a firearm needed a replacement, the entire firearm either had to be sent to an expert gunsmith for custom repairs, or discarded and replaced by another firearm. During the 18th and early 19th centuries, the idea of replacing these methods with a system of interchangeable manufacture was gradually developed.[4][5] The development took decades and involved many people.[4][5]

Gribeauval provided patronage to Honoré Blanc, who attempted to implement the Système Gribeauval at the musket level. By around 1778, Honoré Blanc began producing some of the first firearms with interchangeable flint locks, although they were carefully made by craftsmen. Blanc demonstrated in front of a committee of scientists that his muskets could be fitted with flint locks picked at random from a pile of parts.[1]

Muskets with interchangeable locks caught the attention of Thomas Jefferson through the efforts of Honoré Blanc when Jefferson was Ambassador to France in 1785. Jefferson tried to persuade Blanc to move to America, but was not successful, so he wrote to the American Secretary of War with the idea, and when he returned to the USA he worked to fund its development. President George Washington approved of the idea, and by 1798 a contract was issued to Eli Whitney for 12,000 muskets built under the new system.[6]

Louis de Tousard, who fled the French Revolution, joined the U.S. Corp of Artillerists in 1795 and wrote an influential artillerist's manual that stressed the importance of standardization.[1]


Numerous inventors began to try to implement the principle Blanc had described. The development of the machine tools and manufacturing practices required would be a great expense to the U.S. Ordnance Department, and for some years while trying to achieve interchangeability, the firearms produced cost more to manufacture. By 1853, there was evidence that interchangeable parts, then perfected by the Federal Armories, led to savings. The Ordnance Department freely shared the techniques used with outside suppliers.[1]

Eli Whitney and an early attempt

In the US, Eli Whitney saw the potential benefit of developing "interchangeable parts" for the firearms of the United States military. In July 1801 he built ten guns, all containing the same exact parts and mechanisms, then disassembled them before the United States Congress. He placed the parts in a mixed pile and, with help, reassembled all of the firearms right in front of Congress, much like Blanc had done some years before.[7]

The Congress was captivated and ordered a standard for all United States equipment. The use of interchangeable parts removed the problems of earlier eras concerning the difficulty or impossibility of producing new parts for old equipment. If one firearm part failed, another could be ordered, and the firearm would not have to be discarded. The catch was that Whitney's guns were costly and handmade by skilled workmen.

Charles Fitch credited Whitney with successfully executing a firearms contract with interchangeable parts using the American System,[4] but historians Merritt Roe Smith and Robert B. Gordon have since determined that Whitney never actually achieved interchangeable parts manufacturing. His family's arms company, however, did so after his death.

Brunel's sailing blocks

A pulley block for rigging on a sailing ship

Mass production using interchangeable parts was first achieved in 1803 by Marc Isambard Brunel in cooperation with Henry Maudslay and Simon Goodrich, under the management of (and with contributions by) Brigadier-General Sir Samuel Bentham, the Inspector General of Naval Works at Portsmouth Block Mills, Portsmouth Dockyard, Hampshire, England. At the time, the Napoleonic War was at its height, and the Royal Navy was in a state of expansion that required 100,000 pulley blocks to be manufactured a year. Bentham had already achieved remarkable efficiency at the docks by introducing power-driven machinery and reorganising the dockyard system.

Marc Brunel, a pioneering engineer, and Maudslay, a founding father of machine tool technology who had developed the first industrially practical screw-cutting lathe in 1800 which standardized screw thread sizes for the first time,[8] collaborated on plans to manufacture block-making machinery; the proposal was submitted to the Admiralty who agreed to commission his services. By 1805, the dockyard had been fully updated with the revolutionary, purpose-built machinery at a time when products were still built individually with different components. A total of 45 machines were required to perform 22 processes on the blocks, which could be made in three different sizes. The machines were almost entirely made of metal thus improving their accuracy and durability. The machines would make markings and indentations on the blocks to ensure alignment throughout the process. One of the many advantages of this new method was the increase in labour productivity due to the less labour-intensive requirements of managing the machinery. Richard Beamish, assistant to Brunel's son and engineer, Isambard Kingdom Brunel, wrote:

So that ten men, by the aid of this machinery, can accomplish with uniformity, celerity and ease, what formerly required the uncertain labour of one hundred and ten.

By 1808, annual production had reached 130,000 blocks and some of the equipment was still in operation as late as the mid-twentieth century.[9][10][11][12][13][14][15][16][17][18]

Terry's clocks: success in wood

Wooden Gear
A wooden gear from one of Terry's tall case clocks, showing the use of milled teeth.

Eli Terry was using interchangeable parts using a milling machine as early as 1800. Ward Francillon, a horologist concluded in a study that Terry had already accomplished interchangeable parts as early as 1800. The study examined several of Terry's clocks produced between 1800-1807. The parts were labeled and interchanged as needed. The study concluded that all clock pieces were interchangeable. The very first mass production using interchangeable parts in America was Eli Terry's 1806 Porter Contract, which called for the production of 4000 clocks in three years.[19] During this contract, Terry crafted four-thousand wooden gear tall case movements, at a time when the annual average was about a dozen.[20] Unlike Eli Whitney, Terry manufactured his products without government funding. Terry saw the potential of clocks becoming a household object. With the use of a milling machine, Terry was able to mass-produce clock wheels and plates a few dozen at the same time. Jigs and templates were used to make uniform pinions, so that all parts could be assembled using an Assembly Line.[20]

North and Hall: success in metal

The crucial step toward interchangeability in metal parts was taken by Simeon North, working only a few miles from Eli Terry. North created one of the world's first true milling machines to do metal shaping that had been done by hand with a file. Diana Muir believes that North's milling machine was online around 1816.[21] Muir, Merritt Roe Smith, and Robert B. Gordon all agree that before 1832 both Simeon North and John Hall were able to mass-produce complex machines with moving parts (guns) using a system that entailed the use of rough-forged parts, with a milling machine that milled the parts to near-correct size, and that were then "filed to gage by hand with the aid of filing jigs."[22]

Historians differ over the question of whether Hall or North made the crucial improvement. Merrit Roe Smith believes that it was done by Hall.[23][24] Muir demonstrates the close personal ties and professional alliances between Simeon North and neighboring mechanics mass-producing wooden clocks to argue that the process for manufacturing guns with interchangeable parts was most probably devised by North in emulation of the successful methods used in mass-producing clocks.[21] It may not be possible to resolve the question with absolute certainty unless documents now unknown should surface in the future.

Late 19th and early 20th centuries: dissemination throughout manufacturing

Skilled engineers and machinists, many with armory experience, spread interchangeable manufacturing techniques to other American industries including clockmakers and sewing machine manufacturers Wilcox and Gibbs and Wheeler and Wilson, who used interchangeable parts before 1860.[1][25] Late to adopt the interchangeable system were Singer Corporation sewing machine (1870s), reaper manufacturer McCormick Harvesting Machine Company (1870s–1880s)[1] and several large steam engine manufacturers such as Corliss (mid-1880s)[26] as well as locomotive makers. Typewriters followed some years later. Then large scale production of bicycles in the 1880s began to use the interchangeable system.[1]

During these decades, true interchangeability grew from a scarce and difficult achievement into an everyday capability throughout the manufacturing industries.[27] In the 1950s and 1960s, historians of technology broadened the world's understanding of the history of the development. Few people outside that academic discipline knew much about the topic until as recently as the 1980s and 1990s, when the academic knowledge began finding wider audiences. As recently as the 1960s, when Alfred P. Sloan published his famous memoir and management treatise, My Years with General Motors, even the longtime president and chair of the largest manufacturing enterprise that had ever existed knew very little about the history of the development, other than to say that

[Henry M. Leland was], I believe, one of those mainly responsible for bringing the technique of interchangeable parts into automobile manufacturing. […] It has been called to my attention that Eli Whitney, long before, had started the development of interchangeable parts in connection with the manufacture of guns, a fact which suggests a line of descent from Whitney to Leland to the automobile industry.[28]

One of the better-known books on the subject, which was first published in 1984 and has enjoyed a readership beyond academia, has been David A. Hounshell's From the American System to Mass Production, 1800–1932: The Development of Manufacturing Technology in the United States.[27]

Socioeconomic context

The principle of interchangeable parts flourished and developed throughout the 19th century, and led to mass production in many industries. It was based on the use of templates and other jigs and fixtures, applied by semi-skilled labor using machine tools to augment (and later largely replace) the traditional hand tools. Throughout this century there was much development work to be done in creating gauges, measuring tools (such as calipers and micrometers), standards (such as those for screw threads), and processes (such as scientific management), but the principle of interchangeability remained constant. With the introduction of the assembly line at the beginning of the 20th century, interchangeable parts became ubiquitous elements of manufacturing.

Selective assembly

Interchangeability relies on parts' dimensions falling within the tolerance range. The most common mode of assembly is to design and manufacture such that, as long as each part that reaches assembly is within tolerance, the mating of parts can be totally random. This has value for all the reasons already discussed earlier.

There is another mode of assembly, called "selective assembly", which gives up some of the randomness capability in trade-off for other value. There are two main areas of application that benefit economically from selective assembly: when tolerance ranges are so tight that they cannot quite be held reliably (making the total randomness unavailable); and when tolerance ranges can be reliably held, but the fit and finish of the final assembly is being maximized by voluntarily giving up some of the randomness (which makes it available but not ideally desirable). In either case the principle of selective assembly is the same: parts are selected for mating, rather than being mated at random. As the parts are inspected, they are graded out into separate bins based on what end of the range they fall in (or violate). Falling within the high or low end of a range is usually called being heavy or light; violating the high or low end of a range is usually called being oversize or undersize. Examples are given below.

French and Vierck[29] provide a one-paragraph description of selective assembly that aptly summarizes the concept.

One might ask, if parts must be selected for mating, then what makes selective assembly any different from the oldest craft methods? But there is in fact a significant difference. Selective assembly merely grades the parts into several ranges; within each range, there is still random interchangeability. This is quite different from the older method of fitting by a craftsman, where each mated set of parts is specifically filed to fit each part with a specific, unique counterpart.

Random assembly not available: oversize and undersize parts

In contexts where the application requires extremely tight (narrow) tolerance ranges, the requirement may push slightly past the limit of the ability of the machining and other processes (stamping, rolling, bending, etc.) to stay within the range. In such cases, selective assembly is used to compensate for a lack of total interchangeability among the parts. Thus, for a pin that must have a sliding fit in its hole (free but not sloppy), the dimension may be spec'd as 12.00 +0 −0.01 mm for the pin, and 12.00 +.01 −0 for the hole. Pins that came out oversize (say a pin at 12.003mm diameter) are not necessarily scrap, but they can only be mated with counterparts that also came out oversize (say a hole at 12.013mm). The same is then true for matching undersize parts with undersize counterparts. Inherent in this example is that for this product's application, the 12 mm dimension does not require extreme accuracy, but the desired fit between the parts does require good precision (see the article on accuracy and precision). This allows the makers to "cheat a little" on total interchangeability in order to get more value out of the manufacturing effort by reducing the rejection rate (scrap rate). This is a sound engineering decision as long as the application and context support it. For example, for machines for which there is no intention for any future field service of a parts-replacing nature (but rather only simple replacement of the whole unit), this makes good economic sense. It lowers the unit cost of the products, and it does not impede future service work.

An example of a product that might benefit from this approach could be a car transmission where there is no expectation that the field service person will repair the old transmission; instead, he will simply swap in a new one. Therefore, total interchangeability was not absolutely required for the assemblies inside the transmissions. It would have been specified anyway, simply on general principle, except for a certain shaft that required precision so high as to cause great annoyance and high scrap rates in the grinding area, but for which only decent accuracy was required, as long as the fit with its hole was good in every case. Money could be saved by saving many shafts from the scrap bin.

Economic and commercial realities

Examples like the one above are not as common in real commerce as they conceivably could be, mostly because of separation of concerns, where each part of a complex system is expected to give performance that does not make any limiting assumptions about other parts of the system. In the car transmission example, the separation of concerns is that individual firms and customers accept no lack of freedom or options from others in the supply chain. For example, in the car buyer's view, the car manufacturer is "not within its rights" to assume that no field-service mechanic will ever repair the old transmission instead of replacing it. The customer expects that that decision will be preserved for him to make later, at the repair shop, based on which option is less expensive for him at that time (figuring that replacing one shaft is cheaper than replacing a whole transmission). This logic is not always valid in reality; it might have been better for the customer's total ownership cost to pay a lower initial price for the car (especially if the transmission service is covered under the standard warranty for 10 years, and the buyer intends to replace the car before then anyway) than to pay a higher initial price for the car but preserve the option of total interchangeability of every last nut, bolt, and shaft throughout the car (when it is not going to be taken advantage of anyway). But commerce is generally too chaotically multivariate for this logic to prevail, so total interchangeability ends up being specified and achieved even when it adds expense that was "needless" from a holistic view of the commercial system. But this may be avoided to the extent that customers experience the overall value (which their minds can detect and appreciate) without having to understand its logical analysis. Thus buyers of an amazingly affordable car (surprisingly low initial price) will probably never complain that the transmission was not field-serviceable as long as they themselves never had to pay for transmission service in the lifespan of their ownership. This analysis can be important for the manufacturer to understand (even if it is lost on the customer), because he can carve for himself a competitive advantage in the marketplace if he can accurately predict where to "cut corners" in ways that the customer will never have to pay for. Thus he could give himself lower transmission unit cost. However, he must be sure when he does so that the transmissions he's using are reliable, because their replacement, being covered under a long warranty, will be at his expense.

Random assembly available but not ideally desirable: "light" and "heavy" parts

The other main area of application for selective assembly is in contexts where total interchangeability is in fact achieved, but the "fit and finish" of the final products can be enhanced by minimizing the dimensional mismatch between mating parts. Consider another application similar to the one above with the 12 mm pin. But say that in this example, not only is the precision important (to produce the desired fit), but the accuracy is also important (because the 12 mm pin must interact with something else that will have to be accurately sized at 12 mm). Some of the implications of this example are that the rejection rate cannot be lowered; all parts must fall within tolerance range or be scrapped. So there are no savings to be had from salvaging oversize or undersize parts from scrap, then. However, there is still one bit of value to be had from selective assembly: having all the mated pairs have as close to identical sliding fit as possible (as opposed to some tighter fits and some looser fits—all sliding, but with varying resistance).

An example of a product that might benefit from this approach could be a toolroom-grade machine tool, where not only is the accuracy highly important but also the fit and finish.

See also


  1. ^ a b c d e f g h Hounshell, David A. (1984), From the American System to Mass Production, 1800-1932: The Development of Manufacturing Technology in the United States, Baltimore, Maryland: Johns Hopkins University Press, ISBN 978-0-8018-2975-8, LCCN 83016269
  2. ^ Ford, Henry; Crowther, Samuel (1930), Edison as I Know Him (PDF), New York: Cosmopolitan Book Company, p. 30
  3. ^ Rome, Carthage, and the Punic Wars
    Meanwhile Carthage was mass producing warships. And that's not an exaggeration either about numbers or about shipbuilding methods; Carthaginian warships were built up of standard interchangeable parts. We know this not only from contemporary accounts, but also from recovered Carthaginian ships like the half of a Carthaginian ship shown in (c), above, that was recovered off the coast of Marsala at the western tip of Sicily; it was brand new when it was sunk by the Romans, and it still retains marks giving assembly instructions ("tab a into slot b", etc.) Other recovered ships had identical parts.
  4. ^ a b c Fitch 1882, p. 4.
  5. ^ a b Hounshell 1984, pp. 25–46.
  6. ^ James Burke, Connections (Little, Brown and Co.), 1978/1995 ISBN 0-316-11672-6, p. 150
  7. ^ Van Dusen 2003.
  8. ^ Quentin R. Skrabec, Jr. (2005). "The Metallurgic Age: The Victorian Flowering of Invention and Industrial Science". p. 169. McFarland
  9. ^ "Making the Modern World – Rational manufacture". Retrieved 20 February 2017.
  10. ^ "PORTSMOUTH ROYAL DOCKYARD HISTOR". Retrieved 20 February 2017.
  11. ^ "Archived copy". Archived from the original on 2006-09-24. Retrieved 2006-09-24.CS1 maint: Archived copy as title (link)
  12. ^ Gilbert 1965.
  13. ^ Cooper 1982.
  14. ^ Cooper 1984.
  15. ^ Coad 1989.
  16. ^ Coad 2005.
  17. ^ Wilkin 1999.
  18. ^ Cantrell & Cookson 2002.
  19. ^ Eli Terry and the Connecticut Shelf Clock; Tect
  20. ^ a b Eli Terry and the Connecticut Shelf Clock; Text
  21. ^ a b Muir 2000.
  22. ^ Gordon 1989.
  23. ^ Smith 1973.
  24. ^ Smith 1977.
  25. ^ Thomson, Ross (1989). The Path to Mechanized Shoe Production in the United States. University of North Carolina Press. ISBN 978-0807818671.
  26. ^ Hunter, Louis C. (1985). A History of Industrial Power in the United States, 1730–1930, Vol. 2: Steam Power. Charlottesville: University Press of Virginia.
  27. ^ a b Hounshell 1984.
  28. ^ Sloan 1964, pp. 20–21.
  29. ^ French, Vierck & et al 1953, p. 374.


  • Cantrell, J.; Cookson, G. (eds) (2002), Henry Maudslay and the Pioneers of the Machine Age, StroudCS1 maint: Extra text: authors list (link).
  • Coad, Jonathan (1989), The Royal Dockyards, 1690–1850, Aldershot.
  • Coad, Jonathan (2005), The Portsmouth Block Mills: Bentham, Brunel and the start of the Royal Navy's Industrial Revolution, ISBN 1-873592-87-6.
  • Cooper, C. C. (1982), "The production line at Portsmouth block mill", Industrial Archaeology Review, VI: 28–44.
  • Cooper, C. C. (1984), "The Portsmouth system of manufacture", Technology and Culture, 25 (2): 182–225, doi:10.2307/3104712, JSTOR 3104712.
  • Fitch, Charles H. (1882), Extra Census Bulletin. Report on the manufacture of fire-arms and ammunition, Washington, DC, USA: United States Government Printing Office.
  • French, Thomas E.; Vierck, Charles J.; et al. (1953), A manual of engineering drawing for students and draftsmen (8th ed.), New York, New York, USA: McGraw-Hill, LCCN 52013455.
  • Gilbert, K. R. (1965), The Portsmouth block-making machinery, London, UK.
  • Gordon, Robert B. (1989), "Simeon North, John Hall, and mechanized manufacturing", Technology and Culture, 30 (1): 179–188, doi:10.2307/3105469, JSTOR 3105469.
  • Hounshell, David A. (1984), From the American System to Mass Production, 1800-1932: The Development of Manufacturing Technology in the United States, Baltimore, Maryland: Johns Hopkins University Press, ISBN 978-0-8018-2975-8, LCCN 83016269 Traces in detail the ideal of interchangeable parts, from its origins in 18th-century France, through the gradual development of its practical application via the armory practice ("American system") of the 19th century, to its apex in true mass production beginning in the early 20th century.
  • Muir, Diana (2000), Reflections in Bullough's Pond: Economy and Ecosystem in New England, University Press of New England, ISBN 978-0-87451-909-9.
  • Sloan, Alfred P. (1964), McDonald, John (ed.), My Years with General Motors, Garden City, NY, USA: Doubleday, LCCN 64011306, OCLC 802024. Republished in 1990 with a new introduction by Peter Drucker (ISBN 978-0385042352).
  • Roe, Joseph Wickham (1916), English and American Tool Builders, New Haven, Connecticut: Yale University Press, LCCN 16011753. Reprinted by McGraw-Hill, New York and London, 1926 (LCCN 27-24075); and by Lindsay Publications, Inc., Bradley, Illinois, (ISBN 978-0-917914-73-7). A seminal classic of machine tool history. Extensively cited by later works.
  • Smith, Merritt Roe (October 1973), "John Hall, Simeon North and the Milling Machine", Technology and Culture, 14 (4): 573–591, doi:10.2307/3102444, JSTOR 3102444.
  • Smith, Merritt Roe (1977), Harper's Ferry Armory and the New Technology, Cornell University Press.
  • Van Dusen, Albert E. (2003). "Eli Whitney". Laptop Encyclopedia of Connecticut History. Retrieved 2009-02-18..
  • Wilkin, Susan (1999), The application of emerging new technologies by Portsmouth Dockyard, 1790–1815 [PhD Thesis], The Open University. (Copies available from the British Thesis service of the British Library).

Further reading

External links

American Precision Museum

The American Precision Museum is located in the renovated 1846 Robbins & Lawrence factory on South Main Street in Windsor, Vermont. The building is said to be the first U.S. factory at which precision interchangeable parts were made, giving birth to the precision machine tool industry. In recognition of this history, the building was declared a National Historic Landmark in 1966.A "machine tool" is a machine which makes parts to other machines, such as screws or gun stocks, generally without a skilled craftsman doing the precision work. Instead, a machine operator controls the machine as it does the precision work. Lathes, milling machines, and drill presses are precision machine tools. The museum has the largest collection of historically significant machine tools in the United States.

The museum is open daily from 10am until 5pm from Memorial Day Weekend through October.

American system of manufacturing

The American system of manufacturing was a set of manufacturing methods that evolved in the 19th century. The two notable features were the extensive use of interchangeable parts and mechanization for production, which resulted in more efficient use of labor compared to hand methods. The system was also known as armory practice because it was first fully developed in armories, namely, the United States Armories at Springfield in Massachusetts and Harpers Ferry in Virginia (later West Virginia), inside contractors to supply the United States Armed Forces, and various private armories. 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. In the 1850s, the "American system" was contrasted to the British factory system which had evolved over the previous century. Within a few decades, manufacturing technology had evolved further, and the ideas behind the "American" system were in use worldwide. Therefore, in manufacturing today, which is global in the scope of its methods, there is no longer any such distinction.

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.

Since the parts are interchangeable, it was also possible to separate manufacture from assembly, and repair—an example of the division of labor. This meant that all three functions could be carried out by semi-skilled labor: manufacture in smaller factories up the supply chain, assembly on an assembly line in a main factory, and repair in small specialized shops or in the field. The result is that more things could be made, more cheaply, and with higher quality, and those things also could be distributed further, and lasted longer, because repairs were also easier and cheaper. In the case of each function, the system of interchangeable parts typically involved 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.

Assembly line

An assembly line is a manufacturing process (often called a progressive assembly) in which parts (usually interchangeable parts) are added as the semi-finished assembly moves from workstation to workstation where the parts are added in sequence until the final assembly is produced. By mechanically moving the parts to the assembly work and moving the semi-finished assembly from work station to work station, a finished product can be assembled faster and with less labor than by having workers carry parts to a stationary piece for assembly.

Assembly lines are common methods of assembling complex items such as automobiles and other transportation equipment, household appliances and electronic goods.

Cannibalization (parts)

Cannibalization of machine parts, in maintenance of mechanical or electronic systems with interchangeable parts, refers to the practice of removing parts or subsystems necessary for repair from another similar device, rather than from inventory, usually when resources become limited. The source system is usually crippled as a result, if only temporarily, in order to allow the recipient device to function properly again.

Cannibalization is usually due to unavailability of spare parts, due to an emergency, long resupply times, physical distance, or insufficient planning or budget. Cannibalization can also be due to surplus inventory. At the end of World War II a large quantity of high quality, but unusable war surplus equipment such as radar devices made a ready source of parts to build radio equipment.

Compass (drawing tool)

A pair of compasses, also known as a compass, is a technical drawing instrument that can be used for inscribing circles or arcs. As dividers, they can also be used as tools to measure distances, in particular on maps. Compasses can be used for mathematics, drafting, navigation and other purposes.

Compasses are usually made of metal or plastic, and consist of two parts connected by a hinge which can be adjusted to allow the changing of the radius of the circle drawn. Typically one part has a spike at its end, and the other part a pencil, or sometimes a pen.

Prior to computerization, compasses and other tools for manual drafting were often packaged as a "bow set" with interchangeable parts. By the mid-twentieth century, circle templates supplemented the use of compasses. Today these facilities are more often provided by computer-aided design programs, so the physical tools serve mainly a didactic purpose in teaching geometry, technical drawing, etc.

Eli Terry

Eli Terry Sr. (April 13, 1772 – February 24, 1852) was an inventor and clockmaker in Connecticut. He received a United States patent for a shelf clock mechanism. He introduced mass production to the art of clockmaking, which made clocks affordable for the average American citizen. Terry occupies an important place in the beginnings of the development of interchangeable parts manufacturing. Terry is considered the first person in American history to actually accomplish Interchangeable parts with no government funding . Terry became one of the most accomplished mechanics in New England during the early part of the nineteenth century. The village of Terryville, Connecticut is named for his son, Eli Terry Jr.

Eli Whitney

Eli Whitney (December 8, 1765 – January 8, 1825) was an American inventor best known for inventing the cotton gin. This was one of the key inventions of the Industrial Revolution and shaped the economy of the Antebellum South. Whitney's invention made upland short cotton into a profitable crop, which strengthened the economic foundation of slavery in the United States. Despite the social and economic impact of his invention, Whitney lost many profits in legal battles over patent infringement for the cotton gin. Thereafter, he turned his attention into securing contracts with the government in the manufacture of muskets for the newly formed United States Army. He continued making arms and inventing until his death in 1825.

Factory system

The factory system is a method of manufacturing using machinery and division of labour. Because of the high capital cost of machinery and factory buildings, factories were typically privately owned by wealthy individuals who employed the operative labour. Use of machinery with the division of labour reduced the required skill level of workers and also increased the output per worker.

The factory system was first adopted in Britain at the beginning of the Industrial Revolution in the late 18th century and later spread around the world. It replaced the putting-out system. The main characteristic of the factory system is the use of machinery, originally powered by water or steam and later by electricity. Other characteristics of the system mostly derive from the use of machinery or economies of scale, the centralization of factories, and standardization of interchangeable parts.

General purpose technology

General-purpose technologies (GPTs) are technologies that can affect an entire economy (usually at a national or global level),,. GPTs have the potential to drastically alter societies through their impact on pre-existing economic and social structures. Examples include the steam engine, railroad, interchangeable parts, electricity, electronics, material handling, mechanization, control theory (automation), the automobile, the computer, the Internet, medicine, and Artificial Intelligence.

Henry Maudslay

Henry Maudslay (pronunciation and spelling) (22 August 1771 – 14 February 1831) was an English machine tool innovator, tool and die maker, and inventor. He is considered a founding father of machine tool technology. His inventions were an important foundation for the Industrial Revolution.

Maudslay's invention of a metal lathe to cut metal, circa 1800, enabled the manufacture of standard screw thread sizes. Standard screw thread sizes allowed interchangeable parts and the development of mass production.

Honoré Blanc

Honoré Blanc (1736–1801) was a French gunsmith and a pioneer of the use of interchangeable parts. He was born in Avignon in 1736 and apprenticed to the gun-making trade at the age of twelve. His career spanned the decades from circa 1750 to 1801, a time period that included the reigns of Louis XV and Louis XVI, the American Revolution (which received military aid from Louis XVI), the French Revolution, and the French First Republic.

Human relations movement

Human relations movement refers to the researchers of organizational development who study the behaviour of people in groups, particularly in workplace groups and other related concepts in fields such as industrial and organizational psychology. It originated in the 1930s' Hawthorne studies, which examined the effects of social relations, motivation and employee satisfaction on factory productivity. The movement viewed workers in terms of their psychology and fit with companies, rather than as interchangeable parts, and it resulted in the creation of the discipline of human relations management.

Industrial engineering

Industrial engineering is an engineering profession that is concerned with the optimization of complex processes, systems, or organizations by developing, improving and implementing integrated systems of people, money, knowledge, information, equipment, energy and materials.

Industrial engineers use specialized knowledge and skills in the mathematical, physical, and social sciences, together with the principles and methods of engineering analysis and design, to specify, predict, and evaluate the results obtained from systems and processes. From these results, they are able to create new systems, processes or situations for the useful coordination of labour, materials and machines and also improve the quality and productivity of systems, physical or social. Depending on the sub-specialties involved, industrial engineering may also overlap with, operations research, systems engineering, manufacturing engineering, production engineering, management science, management engineering, financial engineering, ergonomics or human factors engineering, safety engineering, or others, depending on the viewpoint or motives of the user.

Even though its underlying concepts overlap considerably with certain business-oriented disciplines, such as operations management, industrial engineering is a longstanding engineering discipline subject to (and eligible for) professional engineering licensure in most jurisdictions.

John H. Hall (gunsmith)

John Hancock Hall (January 4, 1781 – February 26, 1841) was the inventor of the M1819 Hall breech-loading rifle and a mass production innovator.

Mass production

Mass production, also known as flow production or continuous production, is the production of large amounts of standardized products, including and especially on assembly lines. Together with job production and batch production, it is one of the three main production methods.The term mass production was popularized by a 1926 article in the Encyclopædia Britannica supplement that was written based on correspondence with Ford Motor Company. The New York Times used the term in the title of an article that appeared before publication of the Britannica article.The concepts of mass production are applied to various kinds of products, from fluids and particulates handled in bulk (such as food, fuel, chemicals, and mined minerals) to discrete solid parts (such as fasteners) to assemblies of such parts (such as household appliances and automobiles).

Mass production is a diverse field, but it can generally be contrasted with craft production or distributed manufacturing. Some mass production techniques, such as standardized sizes and production lines, predate the Industrial Revolution by many centuries; however, it was not until the introduction of machine tools and techniques to produce interchangeable parts were developed in the mid 19th century that modern mass production was possible.

Oldsmobile Curved Dash

The gasoline-powered Curved Dash Oldsmobile is credited as being the first mass-produced automobile, meaning that it was built on an assembly line using interchangeable parts. It was introduced by the Oldsmobile company in 1901 and produced through 1907; 425 were produced the first year, 2,500 in 1902, and over 19,000 were built in all. When General Motors assumed operations from Ransom E. Olds on November 12, 1908, GM introduced the Oldsmobile Model 20, which was the 1908 Buick Model 10 with a stretched wheelbase and minor exterior changes.It was a runabout model, could seat two passengers, and sold for US$650. While competitive, due to high volume, and priced below the US$850 two-seat Ford Model C "Doctor's Car", it was more expensive than the Western 1905 Gale Model A roadster at US$500. The Black sold for $375, and the Success for US$250.The flat-mounted, water-cooled, single-cylinder engine, situated at the center of the car, produced 5 hp (3.7 kW), relying on a brass gravity feed carburetor. The transmission was a semiautomatic design with two forward speeds and one reverse. The low-speed forward and reverse gear system is a planetary type (epicyclic). The car weighed 850 lb (390 kg) and used Concord springs. It had a top speed of 20 mph (32 km/h).The car's success was partially by accident; in 1901, a fire destroyed a number of other models before they could be approved for production, leaving the Curved Dash as the only one intact.

Reflections in Bullough's Pond

Reflections in Bullough's Pond: Economy and Ecosystem in New England is a book by Diana Muir. The Providence Journal called Bullough’s Pond "a masterpiece," and Publishers Weekly called it "lyrical". The Massachusetts Center for the Book awarded the 2001 Massachusetts Book Award to Bullough's Pond for the author’s "engaging and accomplished storytelling."

Simeon North

Simeon North (July 13, 1765 – August 25, 1852) was a Middletown, Connecticut, gun manufacturer, who developed one of America's first milling machines (possibly the very first) in 1818 and played an important role in the development of interchangeable parts manufacturing.

North was born in Berlin, Connecticut, into a prosperous family able to provide all six sons with farms of their own. North was given a farm in Berlin, a gift that enabled him to marry Lucy Savage when he was only twenty-one years old; the couple would have five sons and three daughters. In 1795 the Norths purchased a sawmill located on the brook that ran beside their land. Simeon hired a man to help run it, enlarged the building to house a forge and trip-hammer, and began manufacturing scythes from imported steel. Four years later, he obtained a contract to make pistols and began to add a factory to the mill building.

North's brother-in-law Elisha Cheney was skilled clockmaker, a trade he had learned from his father Benjamin and uncle Timothy Cheney, two of the finest clockmakers in Connecticut. In 1810, Elisha Cheney moved his clock-making shop to the next waterpower site upstream from North. Although Cheney was trained as a maker of fine clocks in brass and other materials, Eli Terry, a clockmaker who had trained as a clockmaker with either Timothy or Benjamin Cheney, had just invented a method of producing the parts for wooden shelf, or pillar-and-scroll clocks that enabled them to be mass-produced using interchangeable parts. Cheney used his new plant to mass-produce parts that manufacturers were turning out in emulation of Eli Terry's innovation. Cheney is known to have also produced screws and small metal parts in his mill for the pistols his brother-in-law was manufacturing just downstream.

North is now generally credited with the invention of the milling machine, the first entirely new type of machine invented in America and one which, by replacing filing, made the production of interchangeable parts practicable.

By 1813, North had signed a government contract to produce 20,000 pistols that specified that parts of the lock had to be completely interchangeable between any of the 20,000 locks: the first contract of which any such evidence exists. It was during this period that North is believed to have invented a milling machine, which was able to shape metal mechanically and thus replaced filing by hand. Historian Diana Muir believes that he accomplished this around 1816. According to Muir's book Reflections in Bullough's Pond, North "was the first arms maker to implement a number of machine production techniques, yet he cautiously halted his pursuit of mass-produced, interchangeable parts" whenever it became apparent that it was uneconomic. For some time, interchangeable-part manufacturing in metal would continue to be a combination of machine-made parts and human skill in filing machined parts to precise size for such high-end uses as military weapons, in which interchangeable parts were worth paying for at high prices (they were worth high prices because an army on campaign could cannibalize damaged weapons for parts).

As North's business grew, he moved it from Berlin to nearby Middletown.

At about that time, North was sent to Captain John H. Hall, superintendent of the federal armory at Harpers Ferry, Virginia (now in West Virginia), to introduce his methods of achieving interchangeability. In 1828, North received a contract to produce 5,000 Hall rifles with parts interchangeable with those produced at Harpers Ferry. North had a 53-year contractual relationship with the United States Department of War. The report of Charles H. Fitch prepared for the 1880 Census credits North with a key role in developing manufacture with interchangeable parts.

Spare part

A spare part, spare, service part, repair part, or replacement part, is an interchangeable part that is kept in an inventory and used for the repair or replacement of failed units. Spare parts are an important feature of logistics engineering and supply chain management, often comprising dedicated spare parts management systems.

Capital spares are spare parts which, although acknowledged to have a long life or a small chance of failure, would cause a long shutdown of equipment because it would take a long time to get a replacement for them.

Spare parts are an outgrowth of the industrial development of interchangeable parts and mass production.

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