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Introducing engineering
Introducing engineering

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1.2.3 Muskets and mass production

Achieving interchangeability was an essential breakthrough to mass production. Look around your room right now; you will see many artefacts which have been assembled from parts: your furniture is likely to have been made this way for example. Whether the parts have to be made to fit accurately, as with the ball in the ballpoint pen, or can be a sloppy fit with gaps filled with glue (as with furniture, if gaps and glue are hidden from the eye) will depend on the function to be met by the product.

Close-tolerance interchangeability was achieved in manufacturing only after a long and difficult path. It is now a characteristic difference between industrial and craft manufacture: essentially it can only realistically be achieved by machine-made parts.

It is perhaps unfortunate that many major developments in engineering have come about as a consequence of war. Tremendous efforts were made towards interchangeability in the state armaments industry of eighteenth-century France, but with very limited success. The infantry weapon of the time was the muzzle-loaded musket, where the gun was loaded by pouring gunpowder down the barrel, and shoving the ball (the precursor of the modern bullet) down on top. The gunpowder charge was detonated by a spark caused by a flint striking a steel plate, and the 'flintlock' was a critical sub-system of the gun.

Described image
Figure 11 French M1777 musket, the white box highlights the lock mechanism

The lock was a complex assembly of levers, pivots, plates and springs – some twenty parts in all. To equip a large army, many thousands had to be made, and this task fell to the esteemed profession of the locksmith. (Note that the 'lock' in 'locksmith' refers to the gun mechanism, rather than the door-fastening mechanism of modern usage.)

Master locksmiths first forged the parts from iron stock, and then complete locks would be made by sorting through piles of component parts to find a combination that could be made to fit together and work – with some judicious application of the file along the way. Thus, to make a working lock required a good deal of hand-filing and assembly (using hired labour); each lock was an individual mechanism, and the parts were rarely interchangeable between locks. Imagine how unfeasible such methods would be for the manufacture of the disposable ballpoint pen.

Production rates by such methods were very slow, so there were several hundred craftsmen in the trade working in small groups in workshops scattered around the armament factories. Locksmiths were highly skilled, and would protect their own interests, which they naturally saw as preserving the status quo. However, in 1723,

at the Hôtel des Invalides, in front of august witnesses, Guillaume Deschamps disassembled fifty flintlocks and recombined their parts to produce fifty functioning flintlocks. The minister of war ordered Vallière [a French artillery officer] to supervise the inventor's attempts to expand his system. By 1727 Deschamps had manufactured 660 locks judged interchangeable by Vallière's own inspectors, 'all properly reassembled without a single stroke of the file'. Each lock, however, had cost five times the current price. Undaunted, Deschamps proposed a larger manufacture to produce 5000 identical gunlocks, which he expected to cost only one twentieth of the current price. Tasks were to be divided among specialist workers, who would use dies, gauges and filing jigs to shape parts precisely. Master pattern locks would be distributed to the War Office, Grand Master, inspector, controller and examiner. Deschamps noted that with six hundred locksmiths in the St. Etienne region, he could locally staff a manufacture to produce 40 000 gunlocks a year.

(Alder, 1999, p. 221)

In fact none of this came to pass. In spite of the advantages of the new process, both in the initial assembly of guns and in their subsequent repair, especially in the field, it was by no means clear that productivity could be increased or unit costs brought down. Indeed it took locksmiths longer to make parts which all matched the gauges than to make sets which could be individually assembled functionally. With large quantities of parts being made by the existing routes, it was always possible to find a set of components that would fit together suitably, even if this meant no interchangeability from one lock to the next. The locksmiths were also less than cooperative towards the introduction of the new process, fearing that their craft was being de-skilled so that they would lose their powerful position. Nor were the administrative and technical problems of organising the dispersed skilled labour force easy to overcome.

Fifty years later we read of Honoré Blanc, controller of musket production at the three factories in France, repeating the demonstration of interchangeability with the locks of the standard French musket known as the M1777. The same arguments raged and little was done. Eventually, in post-revolutionary France at Blanc's own manufacturing base at Roanne, interchangeability of flintlock parts was achieved on a large scale. New organisations of the processes, new divisions of labour and new machines contrived to keep the costs of interchangeable locks to no worse than 30% greater than the individual locks made by the old methods. When Napoleon's armies marched across Europe, the bases of mass production had been set.