Löwenherz thread

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The Löwenherz thread is a largely obsolete metric thread form designed in the late nineteenth century and frequently applied in precision instruments. It is named after Dr. Leopold Löwenherz, who was the director of the metrology institute Physikalisch-Technische Bundesanstalt in Berlin. [1]

Metrology science of measurement and its application

Metrology is the science of measurement. It establishes a common understanding of units, crucial in linking human activities. Modern metrology has its roots in the French Revolution's political motivation to standardise units in France, when a length standard taken from a natural source was proposed. This led to the creation of the decimal-based metric system in 1795, establishing a set of standards for other types of measurements. Several other countries adopted the metric system between 1795 and 1875; to ensure conformity between the countries, the Bureau International des Poids et Mesures (BIPM) was established by the Metre Convention. This has evolved into the International System of Units (SI) as a result of a resolution at the 11th Conference Generale des Poids et Mesures (CGPM) in 1960.

Physikalisch-Technische Bundesanstalt national metrology institute of the German Federal Republic

The Physikalisch-Technische Bundesanstalt (PTB) is the national metrology institute of the Federal Republic of Germany, with scientific and technical service tasks. It is a higher federal authority and a public-law institution directly under federal government control, without legal capacity, under the auspices of the Federal Ministry for Economic Affairs and Energy.

Contents

History

In 1888, the Verein Deutscher Ingenieure introduced a thread form that specified threads for diameters from sizes 6 millimeters in diameter to 40 millimeters in diameter. [2] In 1892, at the Congress for Introduction of Standardized Threads for Fixing Screws in Fine Mechanics in Munich, it was decided that the thread form would be truncated. [3] The final form was announced in Berlin in 1894, where the series of thread forms was expanded to include sizes as small as 1 millimeter in diameter. [4]

Verein Deutscher Ingenieure (VDI) is an organization with over 150,000 engineers and natural scientists. More than 12,000 honorary experts process the latest findings every year to promote the technology location. Established in 1856, the VDI is today the largest engineering association in Western Europe. The role of the VDI in Germany is comparable to that of the American Society of Civil Engineers (ASCE) in the United States or Engineers Australia (EA) in Australia barring the broader field of work of the VDI. The VDI is not a union. The association promotes the advancement of technology and represents the interests of engineers and of engineering businesses in Germany.

Munich Capital and most populous city of Bavaria, Germany

Munich is the capital and most populous city of Bavaria, the second most populous German federal state. With a population of around 1.5 million, it is the third-largest city in Germany, after Berlin and Hamburg, as well as the 12th-largest city in the European Union. The city's metropolitan region is home to 6 million people. Straddling the banks of the River Isar north of the Bavarian Alps, it is the seat of the Bavarian administrative region of Upper Bavaria, while being the most densely populated municipality in Germany. Munich is the second-largest city in the Bavarian dialect area, after the Austrian capital of Vienna.

Berlin Capital of Germany

Berlin is the capital and largest city of Germany by both area and population. Its 3,748,148 (2018) inhabitants make it the second most populous city proper of the European Union after London. The city is one of Germany's 16 federal states. It is surrounded by the state of Brandenburg, and contiguous with its capital, Potsdam. The two cities are at the center of the Berlin-Brandenburg capital region, which is, with about six million inhabitants and an area of more than 30,000 km², Germany's third-largest metropolitan region after the Rhine-Ruhr and Rhine-Main regions.

Description

The Löwenherz thread form is unique in having a thread pitch angle of 53° 8′ (53.1333°), which is a smaller angle than the ISO metric thread form but a larger angle than the Thury thread form. The unusual angle was chosen so that the pitch would be approximately equal to the thread's triangular height; however, the design was later truncated (flattened) at the roots and crests of the thread by a factor of one-eight the pitch, so the pitch is about 25% larger than the height, and the thread's depth is about 75% the length of its pitch. [5] The Löwenherz fastener is specified for 31 diameters at irregular intervals ranging from 1mm to 40mm, each with a single corresponding pitch. [6] (This further differentiates the Löwenherz thread from the ISO metric thread, where screws must be specified by both their diameter and pitch because multiple pitches exist for a single diameter.) Löwenherz fasteners are assembled using standard metric wrenches or sockets, and often the hex size for bolt heads and nuts is repeated (so 17mm wrenches can be used on both 9mm and 10mm Löwenherz hardware). [7]

The ISO metric screw threads are the worldwide most commonly used type of general-purpose screw thread. They were one of the first international standards agreed when the International Organization for Standardization (ISO) was set up in 1947.

The Swiss-designed Thury screw thread is a metric thread standard that was developed in the late nineteenth century for screws used in scientific and horological instruments. The thread is named after Marc Thury, an engineer and professor at the University of Geneva who contributed heavily to the standard's development.

Applications and competing thread forms

The Löwenherz thread was used extensively in measuring instruments (like micrometers, which achieve greater precision with finer thread pitches) and in shell manufacturing. [8] It was also popular choice for use in optical instruments, especially in Germany. [9] In addition to seeing its use in instruments designed in Germany, Austria and France, [10] the Löwenhetz thread was once adopted by the Bureau of Standards in the United States as a solution to the lack of uniformity in the type of screws used in American-made instruments. [11]

American National Standards Institute non-profit organization in the United States that develops standards

The American National Standards Institute is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organization also coordinates U.S. standards with international standards so that American products can be used worldwide.

As a precision or scientific thread, the Löwenherz form was rivaled by two contemporary forms: Swiss-designed Thury thread and its derivative the British Association thread. In modern applications, the Löwenherz thread has been replaced with the DIN 13 standard for metric screws. [12] ISO fasteners are available in many of the same pitches and diameters as Löwenherz fasteners; however, ISO and Löwenherz fasteners are not directly interchangeable because the difference in the thread geometry prevents proper mating of fastening components (so an M6x1.0 screw could not be safely installed in a hole tapped for a 6mm Löwenherz screw, even thought they share the same pitch and nominal diameter).

British Association screw threads, or BA screw threads, are a largely obsolete set of small screw threads, the largest being 0BA at 6 mm diameter. They were, and to some extent still are, used for miniature instruments and modelling.

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The Unified Thread Standard (UTS) defines a standard thread form and series—along with allowances, tolerances, and designations—for screw threads commonly used in the United States and Canada. It is the main standard for bolts, nuts, and a wide variety of other threaded fasteners used in these countries. It has the same 60° profile as the ISO metric screw thread, but the characteristic dimensions of each UTS thread were chosen as an inch fraction rather than a millimeter value. The UTS is currently controlled by ASME/ANSI in the United States.

Screw thread helical part of screw

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A go-no gauge refers to an inspection tool used to check a workpiece against its allowed tolerances. Its name is derived from two tests: the check involves the workpiece having to pass one test (go) and fail the other (no-go).

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Screw type of fastener characterized by a thread wrapped around a cylinder

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References

  1. "Lowenherz thread." Sizes, Inc. 18 Jan 2011. Web. Accessed 23 Oct 2016. https://sizes.com/tools/thread_Lowenherzl.htm
  2. "Lowenherz thread." Sizes, Inc. 18 Jan 2011. Web. Accessed 23 Oct 2016. https://sizes.com/tools/thread_Lowenherzl.htm
  3. Prandl, Michael. "Löwenherz Thread." International Thread Standards. Apr 2015. Web. Accessed 23 Oct 2016. http://www.gewinde-normen.de/en/loewenherz-thread.html
  4. "Lowenhertz thread." Sizes, Inc. 18 Jan 2011. Web. Accessed 23 Oct 2016. https://sizes.com/tools/thread_Lowenherzl.htm
  5. Sidders, P. A., edited by. Guide to World Screw Threads. New York: Industrial Press, Inc., 1969. pp. 138 https://books.google.com/books?id=db6jBgAAQBAJ&printsec=frontcover#v=onepage&q&f=false
  6. Oberg, Erik. Machinery's Handbook, 29th Edition. Section 9: Threads and Threading. New York: Industrial Press, 2012. pp. 1946 https://books.google.com/books?id=Qm6zBgAAQBAJ&printsec=frontcover#v=onepage&q&f=false
  7. Prandl, Michael. "Löwenherz Thread." International Thread Standards. Apr 2015. Web. Accessed 23 Oct 2016. http://www.gewinde-normen.de/en/loewenherz-thread.html
  8. French, Lester Grey, edited by. "The Lowenherz Thread" Machinery, Vol. 24 (1917-1918). pp. 837 https://books.google.com/books?id=_H5NAAAAYAAJ&printsec=frontcover#v=onepage&q&f=false
  9. Oberg, Erik. Machinery's Handbook, 29th Edition. Section 9: Threads and Threading. New York: Industrial Press, 2012. pp. 1945 https://books.google.com/books?id=Qm6zBgAAQBAJ&printsec=frontcover#v=onepage&q&f=false
  10. "Lowenherz thread." Sizes, Inc. 18 Jan 2011. Web. Accessed 23 Oct 2016. https://sizes.com/tools/thread_Lowenherzl.htm
  11. Jones, Franklin D. Thread Cutting Methods. First Edition. New York: The Industrial Press, 1918. Accessed 23 Oct 2016. pp. 13 https://books.google.com/books?id=F08JAAAAIAAJ&printsec=frontcover#v=onepage&q&f=false
  12. Prandl, Michael. "Löwenherz Thread." International Thread Standards. Apr 2015. Web. Accessed 23 Oct 2016. http://www.gewinde-normen.de/en/loewenherz-thread.html