What is a machine tool?
According to Wikipedia a machine tool is a machine for shaping or machining metal or other rigid materials, usually by cutting, boring, grinding, shearing, or other forms of deformation.
Machine tools employ some sort of tool that does the cutting or shaping. All machine tools have some means of constraining the workpiece and provide a guided movement of the parts of the machine.
Thus the relative movement between the workpiece and the cutting tool (which is called the toolpath) is controlled or constrained by the machine to at least some extent, rather than being entirely “offhand” or “freehand”.
So, machine tools are “machines that help people to make things”.
A few things about machine tools
Many historians of technology consider that true machine tools were born when the toolpath first became guided by the machine itself in some way, at least to some extent, so that direct, freehand human guidance of the toolpath (with hands, feet, or mouth) was no longer the only guidance used in the cutting or forming process.
In this view of the definition, the term, arising at a time when all tools up till then had been hand tools, simply provided a label for “tools that were machines instead of hand tools”.
Early lathes, those prior to the late medieval period, and modern woodworking lathes and potter’s wheels may or may not fall under this definition, depending on how one views the headstock spindle itself; but the earliest historical records of a lathe with direct mechanical control of the cutting tool’s path are of a screw-cutting lathe dating to about 1483.This lathe “produced screw threads out of wood and employed a true compound slide rest”.
History of the machine tools
Forerunners of machine tools included bow drills and potter’s wheels, which had existed in ancient Egypt prior to 2500 BC, and lathes, known to have existed in multiple regions of Europe since at least 1000 to 500 BC.
But it was not until the later Middle Ages and the Age of Enlightenment that the modern concept of a machine tool—a class of machines used as tools in the making of metal parts, and incorporating machine-guided toolpath—began to evolve.
Clockmakers of the Middle Ages and renaissance men such as Leonardo da Vinci helped expand humans’ technological milieu toward the preconditions for industrial machine tools.
During the 18th and 19th centuries, and even in many cases in the 20th, the builders of machine tools tended to be the same people who would then use them to produce the end products (manufactured goods).
However, from these roots also evolved an industry of machine tool builders as we define them today, meaning people who specialize in building machine tools for sale to others.
Historians of machine tools often focus on a handful of major industries that most spurred machine tool development. In order of historical emergence, they have been firearms (small arms and artillery); clocks; textile machinery; steam engines (stationary, marine, rail, and otherwise); sewing machines; bicycles; automobiles; and aircraft.
Others could be included in this list as well, but they tend to be connected with the root causes already listed. For example, rolling-element bearings are an industry of themselves, but this industry’s main drivers of development were the vehicles already listed—trains, bicycles, automobiles, and aircraft; and other industries, such as tractors, farm implements, and tanks, borrowed heavily from those same parent industries.
Needs fulfilled by machine tools
Machine tools filled a need created by textile machinery during the Industrial Revolution in England in the middle to late 1700s. Until that time machinery was made mostly from wood, often including gearing and shafts.
The increase in mechanization required more metal parts, which were usually made of cast iron or wrought iron. Cast iron could be cast in molds for larger parts, such as engine cylinders and gears, but was difficult to work with a file and could not be hammered. Red hot wrought iron could be hammered into shapes.
Room temperature wrought iron was worked with a file and chisel and could be made into gears and other complex parts; however, hand working lacked precision and was a slow and expensive process.
The advance of machine tools
The advance in the accuracy of machine tools can be traced to Henry Maudslay and refined by Joseph Whitworth. That Maudslay had established the manufacture and use of master plane gages in his shop (Maudslay & Field) located on Westminster Road south of the Thames River in London about 1809, was attested to by James Nasmyth who was employed by Maudslay in 1829 and Nasmyth documented their use in his autobiography.
The process by which the master plane gages were produced dates back to antiquity but was refined to an unprecedented degree in the Maudslay shop. The process begins with three plates each given an identification (ex., 1,2 and 3).
The first step is to rub plates 1 and 2 together with a marking medium (called bluing today) revealing the high spots which would be removed by hand scraping with a steel scraper, until no irregularities were visible. This would not produce absolutely true plane surfaces but a “ball and socket” fit, as this mechanical fit, like two perfect planes, can slide over each other and reveal no high spots.
Next, plate number 3 would be compared and scraped to conform to plate number 1. In this manner plates number 2 and 3 would be identical. Next plates number 2 and 3 would be checked against each other to determine what condition existed, either both plates were “balls” or “sockets”.
These would then be scraped until no high spots existed and then compared to plate number 1. After repeating this process, comparing and scraping the three plates together, they would automatically generate exact true plane surfaces accurate to within millionths of an inch.
The traditional method of producing the surface gages used an abrasive powder rubbed between the plates to remove the high spots, but it was Whitworth who contributed the refinement of replacing the grinding with hand scraping.
Sometime after 1825 Whitworth went to work for Maudslay and it was there that Whitworth perfected the hand scraping of master surface plane gages. In his paper presented to the British Association for the Advancement of Science at Glasgow in 1840, Whitworth pointed out the inherent inaccuracy of grinding due to no control and thus unequal distribution of the abrasive material between the plates which would produce uneven removal of material from the plates.
Joseph Whitworth (21 December 1803 – 22 January 1887)
With the creation of master plane gages of such high accuracy, all critical components of machine tools (i.e., guiding surfaces such as machine ways) could then be compared against them and scraped to the desired accuracy.
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