4 The American System of Manufacture.

While the English were evolving a system of manufacture around the ethos of accuracy, a new system, based on precision and interchangeability of parts was being developed in the United States. The difference occurred because in the English System mechanics and engineers made parts to fit (i.e., to mate with one another) as closely as possible, while interchangeability, by contrast, relies on the existence of clearance between parts. In the English System, the better the fit, the better the workmanship, with "perfection" being the objective. As "fit" was achieved by concentrating on the relationship between components, one made parts for each subassembly one at a time. (1) The parts being assembled were then filed by hand until the mated surfaces fit tightly. The result is that each part and each subassembly are unique.

The greater the clearance between mating surfaces, the more likely parts will be interchangeable. Thus, the objective of interchangeable manufacture was to move from perfection of fit towards the greatest possible clearance, as long as the clearance was not too large to lose the functionality of the product. In doing so, the intellectual problem changed from generating perfection of fit by custom filing and fitting to managing clearances between components in large batches. These concerns are at opposite poles.

Clearances allowed for variance, and management of these variances were the hallmark of the American System of Manufacture. Interchangeable manufacture allowed for the separation not only of fabrication and assembly, but also of the different operations in fabrication from one another. Managing variances entailed prescribing limits and then achieving the precision imposed by these limits by developing (1) machinery that was constrained in its operation, and (2) a system of inspection based on gauges that would ensure that fabricated parts were, indeed, interchangeable.

The simultaneous introduction of special purpose machines and systems of gauging and inspection had the effect of reorienting the thinking of engineers away from making individual components towards the development of systems for manufacturing large lots of components. Charles Babbage, in his celebrated work, On the Economy of Machinery and Manufacture, was the first to distinguish the English and American systems on the basis of making versus manufacturing. [6] Engineering problems were radically different between the two systems. The essential feature of precision manufacture was exact duplication utilizing matched or common fixtures, tools, and size gauges. Workpieces were produced to fit these fixtures, tools, and gauges, rather than to exact size relative to a universal standard of measurement. Thus, the accuracy of parts, according to the English System's concept of deviation from engineering drawings, would generally be worse, yet because every part in the lot was consistent, they could be interchanged.

Although the first complete manufacturing system based on interchangeable parts, a system for making pulley blocks, was built by Brunel, Bentham, and Maudslay at Portsmouth in 1795, their achievement did not alter the intellectual ethos of technological achievement in England. Development of the system was left to the Americans. Our concern with interchangeability in America is not with its origins, which are the subject of some debate, but rather with its effects on the nature of work.

The effects of the American System at Beretta, which was introduced in 1860, are summarized in Table 4.1. Output per worker increased by a factor of 3 while number of workers quadrupled and the number of machines grew from 3 to 50. Products became highly standardized, with only three different products made in the factory.

4.1. The Whitney Factory

Eli Whitney, in carrying out a 1798 contract from the United States government for the manufacture of firearms, employed mainly the same techniques as other gunsmiths of the time. His stocks were made by hand shaving and boring and his barrels were forged by hammers upon anvils and finished with rude drills and grindstones. The lock parts (see Figure 4.1) were ground and drilled, filed approximately to patterns, and fitted together. Whitney's innovation was to make the lock parts more uniform by the systematic use of hardened jigs, and to classify the work on a more intelligent and economical basis.

[FIGURE 4.1 OMITTED]

Assembling the lock parts was considered a crucial test of interchangeability. Because they could not be filed or milled after hardening, lock parts were traditionally assembled and fitted while soft, then marked or kept separate to avoid mixing after hardening. In order to be assembled after hardening, lock parts had to be made interchangeable.

Whitney systematized the work of firearms manufacture by making the parts in lots of large numbers and employing unskilled labor to file them, using hardened jigs to constrain their shape. Operations in his factory are described by Wilma Pitchford Hays.

The several parts of the musket were, under this system, carried

along through the various stages of manufacture, in lots of some

hundreds or thousands of each. In their various stages of progress,

they were made to undergo successive operations by machinery,

which not only vastly abridged the labor, but at the same time so

fixed and determined their form and dimensions, as to make

comparatively little skill necessary in manual operations. Such

were the construction and arrangement of this machinery, that it

could be worked by persons of little or no experience, and yet it

performed the work with so much precision, that when, in the

later stages of the process, the several parts of the musket came

to be put together, they were readily adapted to each other, as if

each had been made for its respective fellow. A lot of 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. Thus, Mr.

Whitney reduced a complex business, embracing many ramifications,

almost to a mere succession of simple processes, and was

thereby enabled to make a division of labor among his workmen,

on a principle which was not only more extensive, but also

altogether more philosophical than that pursued in the English

method. 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.

It will be readily seen that under such an arrangement any

person of ordinary capacity would soon acquire sufficient dexterity

to perform a branch of the work. Indeed, so easy did Mr. Whitney

find it to instruct new and inexperienced workmen, that he uniformly

preferred to do so, rather than to attempt to combat the

prejudices of those who had learned the business under a different

system. [14, pp 53-54]

As a means to ensure precision in barrel manufacture, Whitney introduced "go" and "no go" gauges (Figure 4.2). The smaller of the two plugs was to fit into the barrel. If it did not, or if the large plug did fit into it, the barrel was rejected. Imposition of explicit standards improved the quality of arms, and in 1823 the Ordnance Department began requiring the use of go/no go gauges for arms inspection. [12, p 174]

[FIGURE 4.2 OMITTED]

4.2. Of Machines and Men

Of this period, Charles Fitch wrote that

So far as machinery had been introduced, its construction was

rude, and its use exceptional. Hand-shaving and chiseling for the

stocks, and hand-forging, grinding, and hand-filing for the metal

parts, constituted nearly all of the work.

Apart from all consideration of the earliest usage of specific

machines, it must be said that their introduction did not make

itself felt as a great industrial agency until within twenty-five

years past, in instance of which it may be stated that in 1839,

there were at the Springfield armory about six men to one machine,

and the ratio at other works seems to have been equally large; for

of the private armories most reputed for early improvements one is

stated at this time to have had but a single milling-machine, and

that a rude one; and at another armory a single gang-saw

profiling-machine was the principal stocking machine in use. It was

some fifteen years later before the manufacture of milling, edging,

and other important gun machinery was conducted on a scale

sufficiently extensive for the general outfitting of large armories.

[11, p 7]

The use of this machinery coupled with the use of water power to drive it had combined, as we saw in the earlier description of the Whitney factory, to reduce the skill requirements, though not necessarily the cost, of labor. Fitch observed that

Relative to the skill required in the manufacture (of guns), since

most of the work is special and done by the piece, few of the

operatives may, in any case, be placed under the schedule caption

of ordinary laborers. The foremen upon the several jobs or