Eli Whitney and Interchangeable Parts

Whitneyville, CT, and the Eli Whitney Armory on the Mill River, c. 1862.

Whitneyville, CT, and the Eli Whitney Armory on the Mill River, c. 1825, by William Giles Munson, 1827. Source: Eli Whitney Museum.

The clothes you’re wearing at this moment are made of fiber. Since the mid-20th century, man-made fibers have become extremely commonplace in textile manufacture. But in all the previous centuries and millennia of civilization, the only possible source for fibers was nature. Natures bounty in providing these fibers is not remarkably varied: the four fibers that are generally made into clothing have been cotton, silk, wool and flax. Silk and wool are animal products. Cotton and flax are grown in the fields.

Cotton_gin_EWM_2007Of these, the last to be economically manufactured was cotton. The nub of the problem is that the desirable fibers are attached to seeds; in nature, they help the seeds spread on the wind. Removing the seeds from the fibers (or vice-versa) was a difficult manual job, uneconomical for even a slaveholding economy. A Massachusetts man and Yale graduate named Eli Whitney invented a machine that solved this problem, just as industry needed it. That’s what the cotton gin (short for “engine”) did: combed the seeds out of the fibers so the fibers could be spun into threads, then woven into cloth, all of that depending on other machines invented by other New England Yankees (and old-England mechanics, too).

A staccato drumbeat of new inventions in the late 18th Century increased the throughput of textile operations over a thousandfold in 20 years, producing industrialist millionaires overnight across the British Midlands, while exhausting existing cotton supplies from India, and giving the dying institution of slavery a new economic boost in the southern States. The efficiency of this novel textile industry was so great that a British merchant in India could ship the raw cotton from Calcutta and receive back finished cloth that he could sell for less than local mills could produce it. It made Whitney rich, but not as rich as it might have done, as intellectual property protections were weak at the time, and his cotton gin was widely copied.

Eli Whitney, 1822.

Eli Whitney, painted from life in 1822.

Whitney was born in central Massachusetts, in the then-unincorporated town which became Westborough in 1717. His birth house was long gone, but his family’s barn stood, in bad repair, until a vandal burned it down in the 1970s. But he did not stay in central Massachusetts and would be associated most of his life with the Connecticut River Valley and especially the State of Connecticut. The Connecticut River and its tributaries were larger and had more drop than the smaller rivers further east, making them ideal for powering machinery.

Whitney turned to another field of invention, one that was the lifeblood of the Valley: gun manufacturing. He knew that placing gun manufacturing on an industrial footing would require specialization, and the only way to do that would be to have parts so standardized that they would interchange without handwork or fitting. This required several enabling technologies to have reached maturity, such as measuring tools, manufacturing parts with tools and dies rather than forging them by hand, and manufacturing to understood, and drawn-to-scale, tolerances.

The explanation is well laid by Whitney’s son, Eli, Jr., in an 1890 letter to the author of a monograph on the cotton gin: 

His invention of methods for making practical and successful his system of making the parts of arms, and any-other article, often repeated in manufacture, is of the utmost importance to mankind, and is undoubtedly the foundation of the mechanical prosperity of the United States, and the superiority of American manufactures over those of any other country.

I refer to his uniformity system—or making the similar parts of an arm or machine so near alike in shape that they can be used in assembling the piece without working. In 1798, when he proposed to make arms with parts interchangeable, the French and English ordnance departments laughed at the idea as an absurdity, saying that each arm would be a model, etc., and would cost $100; but he soon proved the advantages of his inventions, so that the United States government adopted his system in all the armories under its control.

In 1798, there were very few skilled mechanics in the United States, and this uniformity system enabled the manufacturers to employ unskilled mechanics to great advantage. In1856, the British government, and in 1871 and 1872, the Russian, German, French and Italian governments adopted the uniformity system of m^aking arms, invented by Kli Whitney in 1797-98. It has been worth many millions to the United States and the world, but he received a very trifling compensation, scarcely worth mentioning, and that indirectly. At the present time, guns, clocks, watches, sewing machines, and almost every article of wood or metal which is often repeated, is made on the plan of his uniformity system, and it would be a loss of many millions every year for the manufacturers of the United States to go back to the old European system of manufacture.

Whitney did not patent any aspect of his interchangeable parts work, which goes back to his difficulties with the cotton gin. His working model of the machine was stolen, and broadly duplicated; and he found that his patent, for all the pride in brought him, was practically unenforceable. So he chose trade-secret protections instead.

Whitney saw clearly what exactly was difficult about firearms manufacturing to an interchangeable standard:

A good musket is a complicated engine and difficult to make — difficult of execution because the conformation of most of its parts correspond with no regular geometrical figure.

A “stand of arms” was the flintlock-era term for a musket and its accessories (ramrod and bayonet). The accessories had traditionally been hand-fitted to the gun, too: as strange as it sounds to a modern soldier, if you and the fellow in the next rank inadvertently swapped bayonets, you might both be left unable to fix them. When Whitney got a contract for 10,000 stands of arms, with interchangeable parts, in 1798, he had to start by building his factory.

The conversion of metals into ramrods, bayonets, barrels, locks, and “mountings” took place, broadly speaking, in two stages: the first shaping required heat and the second required cutting tools. Except for the barrels, these two processes at the Whitney Armory took place in buildings on opposite sides of the Mill River. On the east bank were the forge fires for the shaping of parts; on the west bank were the machines and tools for the cutting of parts. It is probable that the welding, grinding, and boring of the barrels all took place on the west bank, although the evidence on this point so far is inconclusive, after which they were test-fired in a proof house on the east bank. In Eli Whitney Jr’s day, the heat-treating operations of case-hardening and annealing also took place on the east bank and a foundry was added to the complex of buildings there, to allow shaping by casting as well as by forging. Conversion of hardwood into shaped and “inletted” gunstocks and of softwood into shipping crates took place on the west bank, as did the assembly of the parts and packing of completed weapons.

This comment, from the Whitney Museum site, is admittedly partly speculative; the historians at the Museum admit that there is scant information about the layout and day-to-day operations of the Armory, and that most of what we know about Federal period firearms production comes from the archives of Springfield Armory, where ordnance officers obsessively recorded and filed information that, if it existed at private plants like Remington’s, Waters’s and Whitney’s, was treated as ephemeral and not saved after the plant was reorganized. Whitney’s plant underwent many changes in its ninety years of arms making. The Whitney scholars warn about giving too much credence to inferences drawn from records at the the more-systematized Springfield, but note that:

In 1825… 195 separate operations in musket production were listed in a report about Springfield Armory, and were identified as performed by hand or by waterpower. The number of operations per part ranged from three for the sear to 24 for the barrel. Among them were, for instance, five for the trigger: forging by hand, trimming by water, filing by hand, polishing by water, and hardening by hand. At the Whitney Armory, as we currently understand the site, if a trigger went through the same sequence, it would be forged in the east bank forge shop, then taken to the west bank machine and filing shop for trimming, filing and polishing, and returned to the east bank for hardening before finally joining other parts of the “mounting” in the stocking shop on the west bank. Each of the other 29 musket parts mentioned in the list would follow its own sequence of journeys back and forth across the Mill River for shaping, cutting, and heat treating. Although this seems an inefficient arrangement by modern standards of industrial engineering, it was a far less awkward situation than the one at Springfield, in which the water-powered operations were a mile away from the hill-top location of the manual operations. Eli Whitney had initially acquainted himself with this difficulty at Springfield before deciding to locate all of his musket production at the mill site instead of using his cotton gin shop on Wooster Street, two miles away, for hand operations.

Whitney’s guns still had a lot of hand work in them. In general, parts that could be turned and screw slots on early Whitney muskets show machine tool work, and flat and irregular parts show hand filing. His key innovation may have been organizing the work by type of work rather than by type of gun part. Workers seem to have been specialized, also: if you were a filer, you were likely to be a filer of lock plates, or of triggers, rather than a generalist. And these filers were paid, apparently, piecework rates.

Some machine tool historians also credit Whitney with the design of the first practical milling machine. While claims of primacy are always hotly disputed, it seems indisputable that he did build and employ such a machine in Whitneyville near the end of his life.

Whitney had several descendants who worked in the firearms industry, and who jealously guarded their famous ancestor’s reputation, which makes sorting out man from myth at this two centuries’ remove fraught with complexity.

Other New England makers, such as Asa Waters and Thomas Blanchard of Millbury, Mass., and Simeon North of Berlin, Conn., were also working on interchangeable parts and repeatable machinery at the same time. Blanchard’s stock “lathe” would be adopted practically universally by gunmakers; North would introduce his system to the national armory at Harper’s Ferry. And while the system of interchangeable parts with sizes confirmed by jigs and gages would come to be called the American System, French ordnance officers including Honoré Blanc had already tried to apply similar concepts to the manufacture of cannons and muskets.  (As is commonly the case, intelligent men see a similar need at a similar time, quite independently, but Jefferson knew of Blanc’s experiments and promoted the US contract to Whitney, so the Frenchman may truly have primacy).

Now, during the life of Eli Whitney (up to 1825) there was a limit to what this “interchangeability” meant. A hammer from one of Waters’s muskets might interchange with another Waters musket, but a Whitney musket, which might have been made to the same specifications from the War Department, would have parts that would interchange only with other Whitney muskets. To make truly interchangeable parts, that would be a future step, one achieved in Springfield, Whitneyville, and other facilities by the late 1840s. And it comes at a price: hand-fitted parts often have very tight clearances that ensure repeatability and accuracy. Machine finished parts are often finished to somewhat more open tolerances, trading some “perfection” in the individual weapon for the undeniable benefit of easy parts replacement and repair (and, perhaps, reduced skills required for assembly workers).

By the US Civil War, American muskets and rifle-muskets were made of fully interchangeable parts, as were French and English arms, and other nations were working to the same goal.

So Whitney’s interchangeability was but a baby step. But we can see the ancestry of today’s highly modular ARs, not to mention today’s international-partsbin-mongrel AKs, in the late-18th-Century efforts of Eli Whitney to build a couple dozen muskets that could be disassembled and reassembled after the parts were jumbled. It was taken as gospel at the time that every part of every gun required hand fitting by a gunsmith.

Eli Whitney, then, was a key figure in the transition of gunmaking from hand artisanship to mass production. And one of the delightful and cool things about the gun culture is that he didn’t eliminate hand artisanship; competition from mass-produced guns forced artisans to either raise their quality above that obtaining in the factory product, or to reinvent themselves as designers of guns for production (as John M. Browning, whose father had been an old-style handcraft gunsmith, did).

2 thoughts on “Eli Whitney and Interchangeable Parts

  1. Daniel E. Watters

    I seem to remember reading a history of Whitney that insinuated that his famous interchangeable parts demonstration of 1801 was a scam to divert attention from the fact that he was a year late in completing his government rifle contract. He hand-worked a bunch of parts until they could interchange, but he wasn’t set up to produce parts at such tolerances on a timely production basis. It took Whitney another eight years after the demonstration to complete his original contract.

    1. Hognose Post author

      That seems likely, actually. As I think we noted in the piece, existing Whitney muskets show machine work primarily on turned parts, and toolmark signs on of hand work on all irregularly shaped parts.

      The History channel has a page that puts it exactly as you did, with a few more details:


      Honoré le Blanc, on the other hand, seems to have been the real deal, and prior to Whitney. Jefferson saw a display of le Blanc’s interchangeability.

      This comment has been edited. A typo in the second sentence was fixed (marked).

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