As Eli Whitney wrote after completing his 1798 contract to produce 10,000 stands of arms, "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."1 The task he had undertaken was precisely that execution, 10,000 times each, of 50 parts of more or less irregular conformation, to make them fit together into smoothly operating firearms, and to make them durable for use by soldiers. To achieve this, he had to begin from scratch at his newly purchased water-power site at Mill Rock, rebuild the dam, install water wheels, and construct buildings to house the operations of converting raw materials metals and wood into "complicated engines."
A "stand of arms" included the musket and its bayonet and ramrod, both of which also had to fit securely and smoothly to the weapon and be durable in use. 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 proofhouse 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.
Over the ninety years of the Whitney Armory's existence, much technological change took place both in metal and wood-working machinery and in metallurgical capabilities. Changes also took place in the designs of the firearms produced. For both reasons, the Armory saw successive periods of renewal of structures and of equipment, which would then grow obsolete and be replaced again. In this process machines and tools were scrapped or recycled, so remaining material evidence concerning what went on inside the Armory buildings is very scarce. So is written evidence in any detail. What is known about the technique of firearms manufacture in the early nineteenth century mostly derives from records of the United States armory at Springfield, Massachusetts, where techniques for specialization and mechanization of work were carried further than in the smaller private arms factories like Whitney's, even if they had originated in the latter places. So caution should guide inferences drawn from Springfield evidence about what specific techniques were in use at the Whitney Armory at any given time.
In 1825, however, 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.2 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.3 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.
Visitors to the Whitney Armory in 1825 and in 1880 would see very different sites but the basic distinction between the functions of the east bank and west bank structures would be the same.
The buildings of the Whitney Armory on the west side of the Mill River were devoted to the machining, finishing, and assembling of parts. In these buildings the Armory workmen made the barrels, drilled, filed and milled the other metal parts to final shape, polished, browned, or blued them, and prepared the wooden stocks for receiving them. Then the whole guns "lock, stock, and barrel" were assembled, inspected, and packed in wooden boxes for shipping.
The west bank structures that Eli Whitney, Sr. built for these purposes before his death in 1825 were totally replaced by Ei Whitney, Jr. before his retirement in 1888. The use of machines and the specialization of labor begun by Whitney, Sr. after 1798 were extended by Whitney, Jr., and the workforce of 40 to 60 expanded to 200 or more. To accommodate these changes during the later years of the Armory, the two large buildings in the area west of the river and north of the footbridge that are visible on the 1825 map have given way to the five large buildings on the 1879 map.
(A) low dam, (B) machine and filing shop, (C) gunstocking shop, (D) (possible) triphammer shop, (E) forging shop, (K) "1860 building", metal-working machinery, (L) "dam building", barrel-making and stocking, (M) milling and turning, (N) steam engine, (O) browning gunbarrels, making boxes, storing patterns, (P) finishing and assembling.
What went on inside the two large buildings of the early Armory? Very little is known in detail about the machinery used at the Armory during the period of its founder, from 1798 to 1825. Eli Whitney himself did not patent or otherwise write descriptions of his machinery, and although his manufactory became something of a tourist attraction, what visitors wrote about it is more enthusiastic than specific. As for direct material evidence, there were no patent models made, and none of the actual machines has survived the 160 years from that period to today.4 It is, generally speaking, rare that old and therefore obsolete factory machines escape being scrapped before they are recognized as having historic interest. An indirect type of material evidence about the machinery has survived in museums and private collections, however, namely some of the nearly 35,000 muskets that were produced at the Armory before 1825. The art of interpreting tooling marks on gun parts, in order to infer their process of manufacture, has made a promising start.
When Whitney first asked for a contract to make muskets for the United States, he wrote:5
"I am persuaded that Machinery moved by water adapted to this Business would greatly diminish the labor and facilitate the Manufacture of the Article. Machines for forging, rolling, floating, [a kind of filing] boreing, Grinding, Polishing, etc. may all be made use of to advantage."
This gives some indication of what his plans were for machinery, but not necessarily what he put into operation. Three years later, however, his ten-year-old nephew Philos Blake wrote that his uncles factory did contain
"a driling machine and a boureing machine to hour berels and a screw machine and too great large buildings, one nothershop and a stocking shop to stocking guns in, a blacksmith shop, and a trip hammer shop and 500 guns done."6
And upon visiting the Whitney Armory two years later, Yale College President Timothy Dwight notes:7
"machinery, moved by water, and remarkably adapted in every instance to the purpose in view, is employed for hammering, cutting, turning, perforating, grinding, polishing, etc. etc."
The next eyewitness account we have of the equipment at the Whitney Armory is over twenty years later: the probate inventory that was made of Whitney's property after his death in January 1825.8 (See Table I.) Since it is simply a listing of items and their value, it does not distinguish clearly between equipment in use and equipment in storage. But since it is a very long list and includes such trifles as vest and coat buttons and "9 bunches fine Brass wire" for 40 cents, it can be assumed to be complete. Among the items located "In the Machine & Filing shop" at the Armory and on the floor below it, were a number of metal-working machines that were probably water-powered, ranging in value from 22 to 400 dollars. For woodworking, however, the Armory seems not to have been mechanized, even though Whitney had earlier alluded to "a machine for boring wood of my own invention."9 By contrast to the metal-working machines listed in the inventory, the items of apparatus for woodworking in the stocking shop were apparently not water-powered, for some are equipped with cranks and all are of much lower value apiece than those in the other building. His gunstock-ers apparently continued to use hand tools to cut the recesses for metal parts into "thoroughly seasoned" gun stocks that were delivered to the Armory from the U.S. government stores, instead of making them with the irregular turning lathe and other gunstocking machines that Thomas Blanchard had invented and were in use at Springfield Armory during the last few years of Whitney's life.10
The probate inventory, then, suggests that Eli Whitney, Sr. did have water-powered metalworking machines trip hammers, drills, shears, lathes for turning and boring, machines for making screws, and machines for grinding and polishing, but no water-powered woodworking machines.
Some daybooks of the early Armory have survived and give clues as to the work processes going on, but are not explicit as to which of them were mechanized. For instance, Eli Whitney paid $114.75 to Phineas Tyler, one of his workers, for filing 459 locks between September 6, 1809 and April 19, 1810, at 25 cents each.11 Apparently such filing was unmechanized, instead of being performed by the machine for "floating" that Whitney's letter to Wolcott in 1798 had envisioned. This can be inferred not only from the absence of any eyewitness report of such a machine, but also by the presence, elsewhere in the 1825 inventory, of some four hundred hand files of 24 different varieties. It has been argued that so many files would be unnecessary in a factory equipped with a machine for filing.12 (Some perspective on this number may be useful: in Springfield Armory in 1809, to complete 100 muskets required using up 104 files, 60 of which were for the lock filing, 6 for stocking.13 At that rate, the files on hand at the Whitney Armory when the inventory was taken in 1825 would be not quite enough for one lot of 500 guns.)
Close inspection of tooling marks on lockparts from Whitney Armory muskets made before 1825 confirms the written clues about hand-filing instead of machining for flat and irregularly curved surfaces. But it also reveals machining for cylindrical shapes, such as screw shanks and tumbler pivots. Such marks have been interpreted to mean that Eli Whitney was using a water-powered hollow mill, perhaps identifiable as either "the screw machine" mentioned by Philos in 1801 and the inventory in 1825, or as the "milling tools" associated with the "nitching machine" in the inventory.14 The slots in the heads of the screws used in these muskets show that they were cut by a circular saw, probably in the "nitching machine". Machine tool historian Edwin Battison has concluded, from the dates of the Whitney muskets he examined, that "there is evidence for moving back the date for the introduction of two specialized types of milling [the circular saw and the hollow mill] in the [American] arms industry to sometime between 1803 and 1809."15
Perhaps more important for Eli Whitney's new manufactory than his water-powered machines were his methods of organizing the work to be performed by hand as well as by machine. Rather than attempt to employ already experienced gunsmiths, who were scarce, Whitney organized the work of making a musket so that it could be performed by workmen with no particular gunsmithing skill. This required analyzing the work and breaking it down into small steps: a division of labor. Although the eyewitness accounts of the early Armory's production system are not detailed, they do explicitly describe a division of labor by type of operation to be performed instead of by the part of the gun being made, which was a more familiar way of dividing the work. Denison Olmsted's 1832 "Memoir of the Life of Eli Whitney" says
In England, the labor of making a musket was divided by making the different workmen the manufacturers of different limbs, while in Mr. Whitney's system the work was divided with reference to its nature, and several workmen performed different operations on the same limb. 16
Thus, where a single handcraft gunsmith would turn, drill, and file a given lock part until it was finished to the point of fitting to the other parts, a worker in Whitney's armory would specialize in drilling, say, or filing or turning all of the different parts, in production lots of 500 or 1000. According to Olmsted
these parts passed through the hands of several different workmen successively, (and in some cases several times returned, at intervals more or less remote, to the hands of the same workman) each performing upon them every time some single and simple operation, by machinery or by hand, until they were completed.17
To enable his workmen to perform one "single and simple operation" at a time, it is thought that Whitney devised a series of what are today called "jigs and fixtures". These fixed the parts and tools into their relative positions for each operation so that the cutting of the part by the tool would be correct.18 A drilling jig, for example, is made so that the workpiece fits under or inside it in only one position, and the drill, passing through holes in the jig, can enter the workpiece at only the desired angles and locations. A filing jig would sandwich a lockplate, for instance, in such a way that the filer could file no farther than the edges of the jig. In the 1825 inventory jigs and fixtures are probably subsumed in the catch-all terms "apparatus" and "appurtenances." Drilling jigs were apparently called "caps," in the inventory and in the label of Whitney's drawing, "Caps for Drilling Heart holes, Tumbler holes & Bridles."
The 18-year interregnum at the Whitney Armory
from 1825 to 1842 has been
The machinery has great neatness and finish, and in its operation evinces a degree of precision and efficiency, which gratifies every curious and intelligent observer... The manufactory has advanced, in these respects, since it has been superintended by Mr. Whitney's nephews, the Messrs. Blakes, and to them it is indebted for some valuable improvements.
One extremely interesting piece of surviving Whitney Armory machinery has been tentatively ascribed to this period: the oldest known milling machine still in existence. Now on display at the New Haven Colony Historical Society, it was found in 1912 in the hayloft of the Whitney barn, and according to the local tradition as recalled by Eli Whitney III, had been made and used by Eli Whitney, Sr.20 This tradition has been disproved by subsequent scholarship, for the machine is not identified in the 1825 probate inventory, and it is not suitable for hollow-milling, which is the only kind of milling recognizable from tool marks on pre-i825 Whitney-made muskets, as discussed above.21 The best present guess as to the date of the Whitneyville miller is around 1827. A plausible suggestion is that it was made as part of a program undertaken by the Blake brothers to update obsolete equipment at the Armory in order to fulfill the Ordnance Department contract that Eli Whitney obtained before he died.22
The Whitney Armory milling machine shares some features with the "straight cutting" machine in use by 1827 at John Hall's rifle works at Harpers Ferry Armory, most notably, its self-acting and automatically stopping feed mechanism. Although it is now missing its belt-driven rotary cutter and the screw-driven moving platform to which the work was fastened, the Whitney Armory miller was capable, if it was indeed like the Hall straight cutting machine, of using either a shaped cutter or straight edged cutter, to produce not only flat surfaces, but also "a great variety of other surfaces both regular and irregular."23
These milling cutters would perform the heavier metal-removing work, reducing the amount of necessary hand-filing to finishing touches only. The milling machine thus saved on files, which were an expensive item of equipment, and on the work time and experience necessary to produce the locks. According to John Hall, one boy attending three or four such machines could "perform more work than ten men with files, in the same time, and with greater accuracy."24 If the Whitneyville milling machine resembled the Hall machine in operation, then it probably saved on files, skilled labor, and time at the Whitney Armory before it was rendered obsolete by a later generation of improved milling machines.
When young Eli Whitney, Jr. took over
management of the Armory in 1842, he set
Thus, his letter book shows drafts of letters in late 1842 and early 1843 like one to a Mr. Rendall at "the Chicopee Falls Shop" in Massachusetts, asking "When will the milling machine you are making be completed, the sooner the better, etc. etc."26 If his father's Armory had lacked machinery for gunstocking, Whitney Jr. made sure he now obtained the latest improved model of Thomas Blanchard's gunstocking lathe, with the capability of roughing out and smoothing the stock in the same machine.27 Besides the milling machine and the irregular lathe, another type of machine that Eli Whitney, Jr. had to obtain that his father had not used for making muskets was a gunbarrel rifling machine, to cut the shallow spiral grooves within the barrel bore of the 1841 rifle.
In late 1846 Samuel Colt asked Eli Whitney, Jr. if he could make 1000 revolvers for himthe Colt-Walker model that was later famous - in three months. By this time Whitney, Jr. was so well equipped that even though he'd never made pistols before, he confidently replied "I can make them....as soon as any establishment in the U. States except one of the public armories, and probably sooner since no Factory has machinery as complete as mine..." He added, however, that "The 1000 cannot be made in 3 months by Any Factory."28
Colt supplied a model and some machinery from his defunct factory in Paterson, New Jersey, and in only six months the 1000 revolvers were finished.29 A few years after this episode, Whitney, Jr. resumed production of revolvers again, this time on his own account. He was diversifying his business into production of civilian as well as military arms. Since Colt had taken the machinery specifically for pistol making with him to set up his new factory in Hartford, Whitney, Jr. had now to re-equip his Armory for pistol production.
For the civilian market, the rationale for absolute inter-changeability of parts was weaker than in production of military arms,30 and Whitney, Jr. advertised "good and serviceable arms not to be subject to government inspection of gauges."31 By this time, the machine tool firms that were emerging in New England were offering machines that were more specialized and capable of much greater precision than those in Whitney, Sr.'s day. The machinery Whitney, Jr. obtained in the 1850s may have included the other surviving milling machine that is said to have been used at the Whitney Armory. It is a "Robertson's Miller," patented in 1852.32
Whitney, Jr. seems to have continued to derive satisfaction from having a factory that was well-equipped with machines, perhaps more than were absolutely necessary. In 1854 he contemplated the possibility of setting up a small shop in Canada for assembling revolvers from parts made at Whitneyville, by outfitting an extra workforce of three men and a boy with "1 slabber, 1 engine lathe, 1 hand lathe, 1 small shaving machine, 2 polishing wheels..." all from "the machinery I have on hand." Although rather discouraged when looking back in 1855 on his 13-year career so far, he counted first on the positive side of things, his "machinery worth now 10 to 12,000 Dolls.," In a final diary entry in 1860 he remarks on having "bo't largely of gun machinery",33 perhaps referring to the machinery he bought at the bankruptcy sale of the Robbins and Lawrence machine-tool company in Windsor, Vermont in 1857, with the intention of reselling what he didn't need at the Armory.34
He also confided to his diary, "I hope to retire from business in 2 years - pretty much," but this was February 22, 1860, and 14 months later the Civil War broke out. With the proceeds of his sale of water rights to the New Haven Water Company, Whitney, Jr. built new buildings on the west bank of the river, equipped them with machinery for production of 1861 model rifle muskets for contracts with the United States and with Connecticut, expanded his workforce to 400 or more, and apparently stopped thinking about early retirement. After he reorganized the business in 1863 as a corporation named the Whitney Arms Company, it was another 25 years before he sold out and retired from arms making in 1888. After the war the Armory's workforce returned to a peace-time level, and Whitney Jr. advertised his excess "new and secondhand" machinery for sale in the summer of 1868. The capabilities of the machines offered - for milling or slabbing, edging, screwmaking, drilling, planing, turning, screw cutting, pistol- and gun-barrel rifling and boring, clamp-milling, and gun-stocking would, it is safe to guess, have impressed Eli Whitney, Sr. and his probate inventory takers of 43 years earlier.
The Whitney Armory buildings located on the east bank of the Mill River were used for forging and casting metal parts. The fires used in these processes were fueled by coal and charcoal kept in the storage sheds lined up at the foot of the steep slope up Whitney Peak. In the later period a building at the end of this line housed the annealing and case-hardening operations. It is thought that the Armory's small powder house and proofing house for testing barrels were also situated at the foot of this slope from the early period onwards, but their precise locations remain uncertain.
The Forging Shop
The forging shop was built by Eli Whitney, Sr. of traprock quarried from East Rock itself. Changes to its water-power system were made in 1820, 1848, and 1860. Inside, water-powered bellows blew the fires of forges set on stone platforms, each with an anvil nearby. At these forges, smiths heated steel and wrought iron rods, which they then hammered by hand into bayonets, ramrods, lock parts, and gun mountings. They used swages, or dies, to achieve the more complicated shapes. A swage is a pair of steel blocks containing cavities in the shape of the upper and lower halves of the desired object. When the end of the heated rod or bar was held between them on the anvil and hammered, it would deform into the shape of the swage cavity. With a series of progressively detailed swages, it was possible to change the shape of the iron bar gradually. Later, waterpowered drop forging machines augmented the smiths' efforts. The forge building lasted well into this century, although it was converted to other uses, with a thick concrete floor covering the forge platforms. It was burnt out by vandals in 1950 and its remains were bulldozed into oblivion in 1970. In 1974, however, archeologists dug where the old pictures and maps showed the forging shop to have been, and excavated some of the forge platforms and the tail race of its water-power system before they had to bury it again.
The Fuel Storage Sheds
In Whitney Armory days, coal and charcoal arrived by scow at the "sea-coal wharf located near the forge, and by wagon. Of the fuel shortage sheds, Benjamin Silliman wrote in 1832,
There are two buildings for fuel; the one for charcoal, and the other for mineral coal; both are finished with great exactness, by selecting smooth natural faces of the trap rock, which are accurately laid in mortar and carefully pointed; the floors are also of firm stone, laid with equal exactness. These store houses stand by the side of the mountain and its foot, and by excavating a road in the bank above, the coal carts are driven up to the gable end of the building, and their loads are discharged into them simply by tipping up the cart.35
The fuel storage sheds, which were probably built at the same time as the forge shop, were remodeled for various purposes after gun-making ended at the site. The surviving shed, in which charcoal was stored for the Armory, has also been known as "the carpenter shop" and, when the Heany Laboratories occupied the site in the twentieth century, as "the transmission shop." But we can still see the heavy stone lintel high in the back wall, where charcoal was dumped through an opening provided in the original design of the building.
A large single-story wooden structure with a monitor roof, the foundry was probably built by Eli Whitney, Jr. at the start of his career at the Armory, when he was tooling up for production of the model 1841 U.S. rifle. Whitney, Jr.'s foundrymen cast gun fittings and pistol frames both of brass and of malleable cast iron, melting them in graphite crucibles inside a long, low furnace, or (for larger batches of iron only) in a high-standing furnace called a cupola. In the 1880s the foundry ceased operation and was used for storage until it was taken down early in this century. The cupola remained standing for years afterward.
The Annealing and Case Hardening Building
An important part of the craft of iron
metallurgy is heat-treatment to obtain the
The ninety years (1798-1888) in which the Whitney Armory was in operation was a period of experimentation and change in the use of metals in manufacturing.36 The managers of the Whitney Armory participated in that experimentation and change. At the beginning of the period, wrought iron was the main constituent of the muskets that Eli Whitney, Sr. and other arms makers were manufacturing. In his day, when steel could only be made in small batches by the cementation or crucible process, it was expensive and used sparingly in arms manufacturing. By the end of the ninety-year period, steel produced by Bessemer and open-hearth methods was rapidly superseding wrought iron for most purposes in arms manufacturing. Eli Whitney, Jr. was in the 1840s among the first to shift from wrought iron to crucible steel in the manufacture of barrels for his guns, and from the 1850s onwards successfully applied the little-understood technique of malleable iron castings to the production of pistol frames and rifle fittings.
A practically extinct species of metal nowadays, wrought iron is nearly pure iron, and is therefore distinct both from cast iron and from steel, which are alloys of iron and carbon. During the Whitney Armory time-span, wrought iron, also called "bar iron," was produced at rolling mills that were associated with blast furnaces early in the century and with puddling furnaces late in the century. The iron masters used rolling mills to supply manufacturers with bars and rods of the sizes they required. One of Whitney, Sr.'s earliest orders to Forbes and Adam, suppliers of rolled iron in the Salisbury district of northwest Connecticut, specified bars of widths 1 5/8, 2 1/2, and 4 1/4 inches, totalling 1000 pounds of "Salisbury best bloomed iron."37 Later on, iron came to the Whitney Armory by way of New York City, from more distant sources in Pennsylvania and in England.
Bar iron was forged into trigger guards, lock
parts, etc. in the forge shop as described above. It was also made into
barrels. In the early period of the Armory, production of a gun barrel
began by heating and hammering a flat iron bar called a "skelp", wrapping
it lengthwise around a solid iron rod, and welding it into a
cylinder.38 Barrel forgers used
water-powered trip hammers for this purpose. Eli Whitney, Sr.'s armory had
a triphammer shop - probably in the west bank complex of buildings -
containing two trip hammers by 1825. After the barrels were welded, they
were ground to final shape and polished on the outside and bored on the
inside, also in west bank buildings
The small amount of carbon in steel (.1% - 1.5%) makes it stronger and harder than wrought iron. The cementation and crucible steel used at the Whitney Armory through much of its 90 years came from Sheffield, England. It was bent into springs; it was hammered into ramrods and bayonets in the forging shop. In the 18405 Eli Whitney, Jr. adopted the use of steel for gun barrels, earlier than did the Springfield Armory. Toward the end of his career, the technique he was using was to bore a hole through a 2" diameter rod of steel one foot long, insert a solid iron rod, and then roll the steel tube out to barrel length in a rolling mill. This operation probably took place in the gun-barrel shop on the west bank of the river.39
Properly speaking, brass is an alloy of copper with zinc, but copper-tin bronze was also sometimes called "brass." In 1803 Eli Whitney, Sr. improved the muskets he was producing under his first contract with the U.S. Ordnance Department, by making their pans of brass instead of iron, so they wouldn't rust in contact with the gunpowder, and in 1808 "caused a mould to be constructed of cast brass" for his friend Benjamin Silliman, who was professor of chemistry at Yale.40 So we know that he had access to facilities for casting brass, but we do not know where they were located. By 1811, the brass industry in nearby Waterbury, Connecticut was getting under way.41 The rolling mills of that growing industry later made brass available to manufacturers in sheets of uniform thickness, enabling young Eli Whitney, Jr. in 1842 to ponder whether to make the barrel bands and other fittings for the 1841 military rifle of cast brass, or of sheet brass. He opted for casting the bands and other fittings "in my own furnace," and hired a brass caster.42 In the foundry that Whitney, Jr. built, brass was melted in crucibles made of clay and graphite, and poured into sand moulds of the proper shapes for the various gun fittings, and for frames of some models of pistol. After cooling, which was rapid for small objects, the brass gun fittings were broken out of the casting sand and the extraneous pieces of brass "gating" broken or sawed off, to be recycled through the melting process. The castings were polished in a tumbler and taken to the west bank buildings to be machined and assembled with other gun parts into a completed weapon.
Malleable cast iron
On many models of military and civilian weapons, fittings were not of brass but of iron. Although forging was the usual technique for shaping iron into fittings, by Eli Whitney, Jr.'s day, an alternative method was available that had been developed in the late 18205 in Newark, N.J., namely, "black-heart" malleable iron casting (named for its appearance when fractured). Ordinary cast iron, which contains 1.5% to 5% carbon, is brittle and therefore an unsuitable material for any object to be hammered during manufacture or use. But prolonged annealing of castings made with iron having an appropriate composition, under controlled temperatures and atmospheric conditions, converts the carbon to graphite, making the castings malleable. Malleable iron castings were adopted for iron work on carriages, where it eventually supplanted wrought iron.
It was perhaps through the carriage industry, which was strong both in Newark and in New Haven, that the technique of making blackheart malleable cast iron spread from New Jersey to Connecticut, and came to the attention of Eli Whitney, Jr. He adopted it for making pistol frames and fittings for long arms in the late 18505 and early 18605. He was able to use the same kind of crucibles and furnace as for brass casting, but he also built a cupola, which was suitable only for melting iron. The malleable iron castings were as strong as wrought iron gun parts and could be drilled and milled as well. They were apparently not case-hardened, as wrought iron parts were. Malleable cast iron did not replace wrought iron for all purposes in Whitney arms: many items, such as hammers, trigger guards and receivers for rifles, continued to be forged and case-hardened after machining.43
In the manufacturing system
developed at American armories during the first half of the 9th century,
quantities of each gun part were produced to be nearly alike as possible, and
assembled to make whole weapons. After American firearms won admiration at (he
Great Exhibition of 1851 held in London, Great Britain adopted "the American
system" at its Royal Small Arms Manufactory in Enfield, using machine-tools from
New England. Figure 1 shows the Enfield rifle with bayonet socket (2), butt
plate (3), ramrod (4), sight (5), and barrel bands (6), (7) and (8).
Figure 2 shows the lock mechanism (A) with hammer (1), mainspring (2), bridle (3), tumbler (4), swivel (5), sear (6), and sear spring (7). (B) shows two views of the trigger guard with trigger (1) and trigger plate (2).