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34-552: John Dopyera was one of 10 siblings born at the closing of the 19th century. His father, Jozef Dopyera, was a miller in Dolná Krupá , Slovakia , where they moved shortly after the birth of John. Gifted in music, Jozef played and constructed his own violins ; the makers of which were popular around Slovakia for their craftsmanship. Under his father's guidance, John built his first fiddle still in his boyhood days in Dolná Krupá. In 1908,

68-436: A hand crank ), working animal (e.g., horse mill ), wind ( windmill ) or water ( watermill ). In modern era, they are usually powered by electricity . The grinding of solid materials occurs through mechanical forces that break up the structure by overcoming the interior bonding forces. After the grinding the state of the solid is changed: the grain size, the grain size disposition and the grain shape. Milling also refers to

102-418: A 28 MW (38,000 HP) motor. A SAG mill with a 44' (13.4m) diameter and a power of 35 MW (47,000 HP) has been designed. Attrition between grinding balls and ore particles causes grinding of finer particles. SAG mills are characterized by their large diameter and short length as compared to ball mills. The inside of the mill is lined with lifting plates to lift the material inside the mill, where it then falls off

136-466: A certain similarity to roller crushers and roller presses for the compacting of powders, but purpose, construction and operation mode are different. Extreme pressure causes the particles inside of the compacted material bed to fracture into finer particles and also causes microfracturing at the grain size level. Compared to ball mills HPGRs achieve a 30 to 50% lower specific energy consumption, although they are not as common as ball mills since they are

170-475: A golden thumb" refers to the profit the miller makes as a result of this skill. The shape of a miller's thumb is said to have the appearance of the head of a fish. The European bullhead ( Cottus gobio ), a freshwater fish, is commonly called a miller's thumb for this reason. Miller (also known as Millar) is a common surname derived from the old English surname Milleiir . The name, and its many other variants, can be found widely across Europe in countries like

204-401: A hopper leads to a material bed between the two rollers. The bearing units of one roller can move linearly and are pressed against the material bed by springs or hydraulic cylinders. The pressures in the material bed are greater than 50 MPa (7,000 PSI ). In general they achieve 100 to 300 MPa. By this the material bed is compacted to a solid volume portion of more than 80%. The roller press has

238-408: A large screw mounted vertically to lift and grind material. In tower mills, there is no cascading action as in standard grinding mills. Stirred mills are also common for mixing quicklime (CaO) into a lime slurry. There are several advantages to the tower mill: low noise, efficient energy usage, and low operating costs. A VSI mill throws rock or ore particles against a wear plate by slinging them from

272-634: A large, fixed stone as a base and another movable stone operated by hand, similar to a mortar and pestle . As technology and millstones (the bedstone and rynd ) improved, more elaborate machines such as watermills and windmills were developed to do the grinding work. These mills harnessed available energy sources including animal, water, wind, and electrical power. Mills are some of the oldest factories in human history, so factories making other items are sometimes known as mills, for example, cotton mills and steel mills . These factory workers are also called millers. The rynd in pre-reformation Scotland

306-632: A length 1.5 to 2.5 times the diameter. The feed is at one end of the cylinder and the discharge is at the other. Ball mills are commonly used in the manufacture of Portland cement and finer grinding stages of mineral processing. Industrial ball mills can be as large as 8.5 m (28 ft) in diameter with a 22 MW motor, drawing approximately 0.0011% of the total world's power (see List of countries by electricity consumption ). However, small versions of ball mills can be found in laboratories where they are used for grinding sample material for quality assurance. The power predictions for ball mills typically use

340-438: A louder guitar. Beauchamp needed a guitar that could be heard over other instruments when played in an orchestra. Dopyera invented a guitar with three aluminum cones called resonators (similar to diaphragms inside a speaker) mounted beneath the bridge, which was much louder than the regular acoustic guitar . The tone of the guitar was rich and metallic. Dopyera and his brothers Rudy and Emil, as well as other investors, founded

374-499: A narrow range of grain sizes and proposed uniting them along a single curve describing what has come to be known as the Hukki relationship . In stirred mills, the Hukki relationship does not apply and instead, experimentation has to be performed to determine any relationship. To evaluate the grinding results the grain size disposition of the source material (1) and of the ground material (2)

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408-427: A new type of guitar design later recognized to be first ever industrially produced electrified Spanish guitar in the world. Dopyera also invented a string-gripping device on acoustic guitars, the forebear to that on all guitars today. Dopyera's later patents included resophonic additions to nearly every string instrument, continued patents for the designs of banjos and violins, including the unique Dopera Bantar , which

442-460: A newer technology. A similar type of intermediate crusher is the edge runner, which consists of a circular pan with two or more heavy wheels known as mullers rotating within it; material to be crushed is shoved underneath the wheels using attached plow blades. A rotating drum causes friction and attrition between rock pebbles and ore particles. May be used where product contamination by iron from steel balls must be avoided. Quartz or silica

476-415: A relatively large amount of energy; for this reason, an experimental method to measure the energy used locally during milling with different machines was recently proposed. Autogenous or autogenic mills are so-called due to the self-grinding of the ore: a rotating drum throws larger rocks of ore in a cascading motion which causes impact breakage of larger rocks and compressive grinding of finer particles. It

510-552: A week-long gathering of resophonic guitar enthusiasts including some of the best bluegrass, blues, and Hawaiian guitar players in the world. The last Dobrofest was in June, 2008. In addition, there is a small museum in Trnava called the Dobro Hall of Fame. Miller A miller is a person who operates a mill , a machine to grind a grain (for example corn or wheat) to make flour . Milling

544-645: Is also noted. In 1961 they patented the Zorko bass, and then sold the design to Ampeg who produced the Baby Bass from 1962 to 1970. The Dopyera brothers later moved to Chicago , where they made millions of dollars with the Valco music company and other business interests. John elected to stay in Los Angeles and continue making instruments. He was never rich, and was famous only among a small circle of people who knew he had invented

578-919: Is among the oldest of human occupations. "Miller", "Milne" and other variants are common surnames, as are their equivalents in other languages around the world (" Melnyk " in Ukrainian , " Meunier " in French , " Müller " or " Mueller " in German , " Mulder " and " Molenaar " in Dutch , " Molnár " in Hungarian , " Molinero " in Spanish , " Molinaro " or " Molinari " in Italian , " Mlinar " in South Slavic languages etc.). Milling existed in hunter-gatherer communities, and later millers were important to

612-412: Is commonly used because it is inexpensive to obtain. A rotating drum causes friction and attrition between steel rods and ore particles. But the term 'rod mill' is also used as a synonym for a slitting mill , which makes rods of iron or other metal. Rod mills are less common than ball mills for grinding minerals. The rods used in the mill, usually a high-carbon steel, can vary in both the length and

646-427: Is needed. Grinding degree is the ratio of the sizes from the grain disposition. There are several definitions for this characteristic value: [REDACTED] In materials processing a grinder is a machine for producing fine particle size reduction through attrition and compressive forces at the grain size level. See also crusher for mechanisms producing larger particles. In general, grinding processes require

680-581: Is similar in operation to a SAG mill as described below but does not use steel balls in the mill. Also known as ROM or "Run Of Mine" grinding. A typical type of fine grinder is the ball mill . A slightly inclined or horizontal rotating cylinder is partially filled with balls , usually stone or metal , which grind material to the necessary fineness by friction and impact with the tumbling balls. Ball mills normally operate with an approximate ball charge of 30%. Ball mills are characterized by their smaller (comparatively) diameter and longer length, and often have

714-760: The National String Instrument Corporation to manufacture the new type of "resophonic" guitar, which was sold mainly to musicians working in cinemas and jazz clubs in the USA. After several years, the three brothers left the corporation and started a new company, Dobro (the name they also gave to the instrument). The new name combined the "Do" in Dopyera and "bro" in brothers—and also means "good" in Slovak. Their slogan was: Dobro means good in any language! . In 1932, working together with Art Stimson, Dopyera invented

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748-408: The development of agriculture . The materials ground by millers are often foodstuffs and particularly grain . The physical grinding of the food allows for the easier digestion of its nutrients and saves wear on the teeth. Non-food substances needed in a fine, powdered form, such as building materials , may be processed by a miller. The most basic tool for a miller was the quern-stone —simply

782-589: The Dopyeras emigrated from Slovakia to California , United States sensing a war would erupt in Europe. In the 1920s, Dopyera opened his own store in Los Angeles where he worked making and repairing fiddles, banjos, and other wooden string instruments. Around this time, Dopyera patented several improvements on the banjo. In 1925, Dopyera was asked by vaudeville instrumentalist (and, later, pioneer developer of electrically amplified instruments) George Beauchamp to create

816-518: The UK, Ireland, and many other countries across the world. Mill (grinding) A mill is a device, often a structure , machine or kitchen appliance , that breaks solid materials into smaller pieces by grinding, crushing, or cutting. Such comminution is an important unit operation in many processes . There are many different types of mills and many types of materials processed in them. Historically mills were powered by hand or by animals (e.g., via

850-419: The city of Ivrea , Italy , commemorates a spirited "Mugnaia" (miller's daughter) who supposedly refused to let a local duke exercise his right of the first night , and proceeded to chop the duke's head off and spark a revolution. Whatever the historical validity of the story, it is significant it was the daughter of a miller to whom folk tradition assigned this rebellious role. As an important part of his job,

884-417: The diameter. However, the smaller the rods, the larger is the total surface area and hence, the greater the grinding efficiency. SAG is an acronym for semi-autogenous grinding. SAG mills are autogenous mills that also use grinding balls like a ball mill. A SAG mill is usually a primary or first stage grinder. SAG mills use a ball charge of 8 to 21%. The largest SAG mill is 42' (12.8m) in diameter, powered by

918-473: The following form of the Bond equation: where Another type of fine grinder commonly used is the French buhrstone mill, which is similar to old-fashioned flour mills . A high pressure grinding roll, often referred to as HPGRs or roller press, consists out of two rollers with the same dimensions, which are rotating against each other with the same circumferential speed. The special feeding of bulk material through

952-472: The following purposes in engineering: In spite of a great number of studies in the field of fracture schemes there is no formula known which connects the technical grinding work with grinding results. Mining engineers, Peter von Rittinger , Friedrich Kick and Fred Chester Bond independently produced equations to relate the needed grinding work to the grain size produced and a fourth engineer, R.T.Hukki suggested that these three equations might each describe

986-411: The miller repeatedly takes into his hand samples of the ground meal coming out of the spout in order to feel the quality and character of the product. The miller rubs the grain between his thumb and forefinger. After years of doing this, the miller's thumb changes shape and becomes broad and flattened. This is known as a "miller's thumb". Sayings such as "worth a millerˈs thumb" and "an honest miller hath

1020-526: The plates onto the rest of the ore charge. SAG mills are primarily used at gold, copper and platinum mines with applications also in the lead, zinc, silver, alumina and nickel industries. Tower mills, often called vertical mills, stirred mills or regrind mills, are a more efficient means of grinding material at smaller particle sizes, and can be used after ball mills in a grinding process. Like ball mills, grinding (steel) balls or pebbles are often added to stirred mills to help grind ore, however these mills contain

1054-527: The process of breaking down, separating, sizing, or classifying aggregate material (e.g. mining ore ). For instance rock crushing or grinding to produce uniform aggregate size for construction purposes, or separation of rock, soil or aggregate material for the purposes of structural fill or land reclamation activities. Aggregate milling processes are also used to remove or separate contamination or moisture from aggregate or soil and to produce "dry fills" prior to transport or structural filling. Grinding may serve

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1088-466: The resonator/resophonic guitar. He died at the age of 94 in 1988, having registered some 40 patents. The Dobro resonator guitar was fundamental to the evolution of bluegrass music. The design cut through all musical boundaries, however, proving equally at home in folk, rock country, blues and jazz. In 1992, Slovak blues guitarist Peter Radványi co-founded the Dobrofestival in western Slovakia's Trnava ,

1122-455: Was a cross between the 5-string Banjo and 6-string Guitar. The Dopera Bantars, though extremely rare were used by a few influential artists of the 1960s, including Bob Dylan . As illustrated with the Bantar, John removed the "Y" from the Dopyera name, when labeling his new instruments, as he reasoned that "Dopera" was easier for the public to understand and pronounce. A patent for an electric violin

1156-451: Was often carved on millers' gravestones as a symbol of their trade. In a traditional rural society, a miller is often wealthier than ordinary peasants, which can lead to jealousy. Millers are often accused of associating with thieves, and were targeted in bread riots at times of famine . Conversely, millers might be in a stronger position vis-a-vis feudal land owners than are ordinary peasants. The traditional carnival held annually in

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