HISTORICAL NOTE The Manufacture of Screws
2
HISTORICAL NOTE The Manufacture of Screws The concept of the screw, both as a fas- tener and as a device to move material, has been known since ancient Greek I times. Not until the age of mechanization, though, were screws produced with enough precision and in sufficient quanti- ties to become crucial components of the development of technology. Screws can be made of iron, steel, cop- per, bronze, brass, aluminum, wood, or hard plastics. Mechanically, a screw is a continuous inclined plane wrapped around a cylinder. Several names are often mentioned in connection with the invention of the screw. The Pythagorean philosopher Archytas of Tarentum is alleged to be the actual inventor of the screw in the fifth century B.C., though the date of the screw's first appearance as a useful me- chanical object is not clear. Archimedes (third century B.C.) is often credited with the invention of the water screw, or "screw of Archimedes," though similar devices appear to have been used for irrigation in Egypt much earlier than this. The Greek scientist Hero, living in Alexandria in the first century A.D., invented a screw press for squeezing olives and grapes to produce olive oil and wine. Turning the shaft of the screw press applied great and constant pressure to the fruit, producing much more liquid than other simple crush presses could. The Romans used the screw press for pressing clothes. A drawing of such a clothes press survived in the ruins of Pompeii from 79 A.D. External screw threads could be made by tediously marking the diagonal chan- nels on a wooden rod, then sawing, and finishing by filing. But cutting the internal thread of a nut or a pipe proved to be problematic. By the first century A.D., taps for cutting or grinding internal threads were also in use. Many centuries later, as technology advanced into the age of mechanization, screws took a more prominent role. For instance, England's large Salisbury clock (made in 1380, and perhaps the oldest clock still operating in the world) was constructed without a single screw; craftsmen used wedges or rivets to hold its iron frame together. The delicate pieces of smaller precision clocks created in later years, though, could not obvious- ly be hammered together, but required small metal screws for assembly. Metal screws and nuts came into use in the 15th century. A hexagonal or square head was turned with a box wrench. A century later, the screws used in armor featured nicks or slots in their round heads, possibly for the use of a screwdriv- er. Centuries later, James Watt (1736- 1819), best known for his invention of the practical steam engine, also designed a screw printing press: A letter written in special ink was screwed up against moist copy sheets for reproduction. In his notebooks, Leonardo da Vinci (1452-1519) sketched a machine for cut- ting screws as well as a screw-operated printing press. The wood screw, which deforms the wood itself into accompanying nut threads, is not mentioned until the mid- 16th century. A different variation, the metal screw, is designed to hold sheets of metal that are thinner than one groove, which obviates the need for making threads inside the material. A mid-16th century mining treatise offhandedly describes a large slot-head screw tapering to a point (for boring into rock), as if it were a common object. But not until the mid-19th century were screws commonly made with pointed ends. Before this time, a hole long enough to accept the full length of the screw was required. An American traveler, George Escol Sellers, took a trip to Britain with instructions from his father "to see and learn all that was accessible in the way of civil and mechanical engineering." Sellers toured many renowned British factories, but he wrote with some amusement how those he encountered resisted the American idea of adding points to screws: "Mr. E.R. Sheer, a pianoforte maker of Philadelphia, in fitting work where wood screws had to be withdrawn and again driven in the same holes had found it dif- ficult to make the common square-end English wood screw enter and follow the thread cut by the first insertion...with file and chasing tool he tapered the end of the screw like that of a gimlet. He had given me several of these as samples, with the request that when in Birmingham I would induce some good screwmaker to fill a considerable order of gimlet-pointed screws. I had gone to the makers...[but] failed to induce any of them to fill the order; they and their predecessors had always made wood screws as they were then doing, and they would have nothing to do with such new-fangled notions." Typically, each screw manufacturer designed the screw threads to his own convenience. Threads cut with a sharp V profile had disadvantages because the weak, pointed crests broke off in small pieces and high stress concentration in the sharp root often caused the screw to fail—resulting in inconvenience, delay, and expense because it was difficult to find a replacement screw that would fit the grooves. In 1841 Sir Joseph Whitworth in England proposed that all screw manu- facturers use a rounded fastening thread with grooves tilted at 55°; this became the British standard thread used for general engineering. In 1864 William Sellers (no relation to George Sellers, mentioned pre- viously) in the United States proposed a screw with a 60° thread, with crests cut off and roots filled in, which was accept- ed as the U.S. standard. In 1948 the United Kingdom, United States, and Canada together adopted the Sellers stan- dard. Screws are mass-produced by turning on a special lathe, where the threads are cut with a single-point cutting tool. Dies for cutting threads, as in pipes, are made with internal cutting edges of the proper size, shape, and pitch. Milling is useful for producing large and accurate threads. Rolling a screw blank between flat or cylindrical dies allows a high rate of production; this method was introduced for manufactur- ing cheap stove bolts, but improvements have made possible the high-volume pro- duction of superior screws and bolts. Today, modern machines create bil- lions of screws and bolts each year. These machines are essentially automatic turret lathes with one or more spindles; each component of the multiple-tool holder is brought into action on a pivot as the man- ufacturing steps proceed: turning and threading bar stock, forming the head, and cutting off the screw or bolt. Special screws can be manufactured by using chasers or comb tools controlled by mas- ter screws. Few simple ideas have had so great an impact on the development of human civ- ilization. KEVIN J. ANDERSON FOR FURTHER READING, consult Nuts and Bolts of the Past: A History of American Technology, 1776-1860, by David Freeman Hawke, Harper & Row, 1988; and The Discoverers by Daniel J. Boorstin, Random House, 1983. 68 MRS BULLETIN/FEBRUARY 1994 https://www.cambridge.org/core/terms. https://doi.org/10.1557/S088376940003935X Downloaded from https://www.cambridge.org/core. IP address: 65.21.228.167, on 20 Mar 2022 at 13:12:42, subject to the Cambridge Core terms of use, available at
Transcript of HISTORICAL NOTE The Manufacture of Screws
HISTORICAL NOTE
The Manufacture of ScrewsThe concept of the screw, both as a fas-
tener and as a device to move material,has been known since ancient Greek
I times. Not until the age of mechanization,though, were screws produced withenough precision and in sufficient quanti-ties to become crucial components of thedevelopment of technology.
Screws can be made of iron, steel, cop-per, bronze, brass, aluminum, wood, orhard plastics. Mechanically, a screw is acontinuous inclined plane wrappedaround a cylinder.
Several names are often mentioned inconnection with the invention of thescrew. The Pythagorean philosopherArchytas of Tarentum is alleged to be theactual inventor of the screw in the fifthcentury B.C., though the date of thescrew's first appearance as a useful me-chanical object is not clear.
Archimedes (third century B.C.) isoften credited with the invention of thewater screw, or "screw of Archimedes,"though similar devices appear to havebeen used for irrigation in Egypt muchearlier than this.
The Greek scientist Hero, living inAlexandria in the first century A.D.,invented a screw press for squeezingolives and grapes to produce olive oil andwine. Turning the shaft of the screw pressapplied great and constant pressure to thefruit, producing much more liquid thanother simple crush presses could. TheRomans used the screw press for pressingclothes. A drawing of such a clothes presssurvived in the ruins of Pompeii from 79A.D.
External screw threads could be madeby tediously marking the diagonal chan-nels on a wooden rod, then sawing, andfinishing by filing. But cutting the internalthread of a nut or a pipe proved to beproblematic. By the first century A.D.,taps for cutting or grinding internalthreads were also in use.
Many centuries later, as technologyadvanced into the age of mechanization,screws took a more prominent role. Forinstance, England's large Salisbury clock(made in 1380, and perhaps the oldestclock still operating in the world) wasconstructed without a single screw;craftsmen used wedges or rivets to holdits iron frame together. The delicatepieces of smaller precision clocks createdin later years, though, could not obvious-ly be hammered together, but requiredsmall metal screws for assembly.
Metal screws and nuts came into use in
the 15th century. A hexagonal or squarehead was turned with a box wrench. Acentury later, the screws used in armorfeatured nicks or slots in their roundheads, possibly for the use of a screwdriv-er. Centuries later, James Watt (1736-1819), best known for his invention of thepractical steam engine, also designed ascrew printing press: A letter written inspecial ink was screwed up against moistcopy sheets for reproduction.
In his notebooks, Leonardo da Vinci(1452-1519) sketched a machine for cut-ting screws as well as a screw-operatedprinting press.
The wood screw, which deforms thewood itself into accompanying nutthreads, is not mentioned until the mid-16th century. A different variation, themetal screw, is designed to hold sheets ofmetal that are thinner than one groove,which obviates the need for makingthreads inside the material.
A mid-16th century mining treatiseoffhandedly describes a large slot-headscrew tapering to a point (for boring intorock), as if it were a common object. Butnot until the mid-19th century werescrews commonly made with pointedends. Before this time, a hole long enoughto accept the full length of the screw wasrequired. An American traveler, GeorgeEscol Sellers, took a trip to Britain withinstructions from his father "to see andlearn all that was accessible in the way ofcivil and mechanical engineering." Sellerstoured many renowned British factories,but he wrote with some amusement howthose he encountered resisted theAmerican idea of adding points toscrews:
"Mr. E.R. Sheer, a pianoforte maker ofPhiladelphia, in fitting work where woodscrews had to be withdrawn and againdriven in the same holes had found it dif-ficult to make the common square-endEnglish wood screw enter and follow thethread cut by the first insertion...with fileand chasing tool he tapered the end of thescrew like that of a gimlet. He had givenme several of these as samples, with therequest that when in Birmingham Iwould induce some good screwmaker tofill a considerable order of gimlet-pointedscrews. I had gone to the makers...[but]failed to induce any of them to fill theorder; they and their predecessors hadalways made wood screws as they werethen doing, and they would have nothingto do with such new-fangled notions."
Typically, each screw manufacturer
designed the screw threads to his ownconvenience. Threads cut with a sharp Vprofile had disadvantages because theweak, pointed crests broke off in smallpieces and high stress concentration inthe sharp root often caused the screw tofail—resulting in inconvenience, delay,and expense because it was difficult tofind a replacement screw that would fitthe grooves.
In 1841 Sir Joseph Whitworth inEngland proposed that all screw manu-facturers use a rounded fastening threadwith grooves tilted at 55°; this became theBritish standard thread used for generalengineering. In 1864 William Sellers (norelation to George Sellers, mentioned pre-viously) in the United States proposed ascrew with a 60° thread, with crests cutoff and roots filled in, which was accept-ed as the U.S. standard. In 1948 theUnited Kingdom, United States, andCanada together adopted the Sellers stan-dard.
Screws are mass-produced by turningon a special lathe, where the threads arecut with a single-point cutting tool. Diesfor cutting threads, as in pipes, are madewith internal cutting edges of the propersize, shape, and pitch.
Milling is useful for producing largeand accurate threads. Rolling a screwblank between flat or cylindrical diesallows a high rate of production; thismethod was introduced for manufactur-ing cheap stove bolts, but improvementshave made possible the high-volume pro-duction of superior screws and bolts.
Today, modern machines create bil-lions of screws and bolts each year. Thesemachines are essentially automatic turretlathes with one or more spindles; eachcomponent of the multiple-tool holder isbrought into action on a pivot as the man-ufacturing steps proceed: turning andthreading bar stock, forming the head,and cutting off the screw or bolt. Specialscrews can be manufactured by usingchasers or comb tools controlled by mas-ter screws.
Few simple ideas have had so great animpact on the development of human civ-ilization.
KEVIN J. ANDERSON
FOR FURTHER READING, consult Nuts andBolts of the Past: A History of AmericanTechnology, 1776-1860, by David FreemanHawke, Harper & Row, 1988; and TheDiscoverers by Daniel J. Boorstin, RandomHouse, 1983.
68 MRS BULLETIN/FEBRUARY 1994
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