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The History of Screwthreads and What the Future Holds in Threading Standards

12/17/2024

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by Bernard Martin
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The history of screw threads highlights innovation, technology, and the pursuit of precision and standardization in engineering. We're going to take a tour of some history that begins with the ancient Greeks and Egyptians, moves through significant developments during the Renaissance,  discusses modern standards and and culminates in a discussion of the potential directions of new applications and standards for screw threads. Grab a cup of coffee and read on.

Ancient Beginnings

Archimedes screw as a form of art by Tony Cragg at 's-Hertogenbosch in the Netherlands
Archimedes screw as a form of art by Tony Cragg at 's-Hertogenbosch in the Netherlands
Greek and Egyptian InnovationsThe use of screw threads dates back to ancient civilizations, notably among the Greeks and Egyptians, who applied screw mechanisms in devices like the water screw for irrigation and olive oil presses. These early screws were primarily wooden and served as vital components in simplifying labor and enhancing the efficiency of agricultural and building projects. The genius of Archimedes, with the invention of the Archimedean screw, exemplifies early engineering innovation, showcasing the practical application of screw threads in lifting water.

Greek Ingenuity: Archytas and Archimedes
The tale begins in ancient Greece, a crucible of scientific thought and mechanical invention. It was here that Archytas of Tarentum, a philosopher, mathematician, and contemporary of Plato, is believed to have devised the first known screw mechanism between 428 BC-350 BC and used them in presses for olives and grapes. Although specific details of Archytas's contributions to screw technology are scarce, his work in understanding mechanics and motion undoubtedly paved the way for subsequent innovations.

Archimedes, often celebrated for his mathematical genius and inventive prowess, is credited with the practical application of the screw principle in the form of the Archimedean screw. This ingenious device, consisting of a helical screw enclosed within a cylinder, was used to transfer water from low-lying bodies into irrigation ditches, proving invaluable for agriculture and the sustenance of civilizations. The Archimedean screw not only exemplifies the application of screw threads in ancient times but also highlights the Greeks' adeptness at leveraging simple mechanical principles for practical ends.

Egyptian Mastery: Building a Civilization
Parallel to Greek advancements, the ancient Egyptians demonstrated remarkable engineering capabilities, integrating screw mechanisms into their technology. Among their many innovations, the use of screw presses for extracting olive oil and wine stands out. These early applications of screw threads were pivotal in agricultural production and the economy, underlining the screw's role in enhancing efficiency and productivity in ancient societies.

The construction of monumental structures like the pyramids further attests to the Egyptians' sophisticated use of technology. While direct evidence of screw threads in these constructions is speculative, the precision and ingenuity required suggest a deep understanding of mechanical principles akin to those employed in screw mechanisms.

The Legacy of Ancient InnovationsThe contributions of ancient Greeks and Egyptians to the development of screw threads are more than historical footnotes; they represent the dawn of mechanical engineering and the human capacity for innovation. These early inventions laid the groundwork for countless technological advancements, illustrating the timeless value of observing, understanding, and applying natural principles.

Renaissance Revival

Precision and ApplicationThe Renaissance was a period of rediscovery and innovation, where the significance of precision in mechanical devices became increasingly recognized. This era saw the refinement of screw-cutting techniques and tools, marking a departure from the manual, less accurate methods of earlier times. The development of screw-cutting lathes during this period was instrumental in the manufacture of more precise and uniform screw threads, laying the groundwork for the advanced mechanical systems of the future.

​This period, characterized by an enthusiastic return to classical knowledge enriched by innovative thinking, laid crucial groundwork for the future of precision mechanics.

​Amidst this intellectual ferment, the development of screw threads took significant strides forward, though not through a uniform march of progress but rather via a patchwork of advancements, each contributing to the incremental improvement of mechanical devices.
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Innovations in Screw-Cutting Techniques
The Renaissance's contribution to screw thread technology was marked by inventive approaches to screw-cutting techniques and the introduction of specialized tools. A noteworthy example of such innovation is the screw-cutting lathe, which, while not invented in the Renaissance, saw significant refinements during this period. The evolution of these lathes can be attributed to the collective efforts of artisans and inventors who sought to standardize and enhance the precision of screw threads, crucial for machinery and instruments.
A man operating a lathe with fixed cutting tool driven by the action of weights; here the machine is cutting screw threads in wood
A man operating a lathe with fixed cutting tool driven by the action of weights; here the machine is cutting screw threads in wood. 1578. Library of Congress Rare Book and Special Collections Division Washington, D.C. 20540 USA

Notable Contributors and Their Legacy​
Leonardo da Vinci
Leonardo da Vinci, a polymath whose interests spanned various fields, contributed to the development of screw thread technology through his designs and sketches. Da Vinci's codices include illustrations of machine elements with screw threads, indicating his understanding of their importance in mechanical design. Although there is no direct evidence of da Vinci constructing a screw-cutting machine, his detailed drawings suggest a theoretical groundwork for later advancements

Jacques Besson
Jacques Besson, a French engineer and inventor in the late Renaissance, contributed significantly with his book "Theatre des Instruments Mathematiques et Mechaniques." Published in 1578, this work illustrated various machines, including a screw-cutting lathe that showcased an early attempt at automating the production of screw threads. Besson's designs represented a leap towards the precision and standardization sought by later inventors.

The Impact of the Scientific Revolution
The Renaissance set the stage for the Scientific Revolution, which in turn influenced mechanical engineering and the development of screw threads. The period's emphasis on empirical evidence and the questioning of established knowledge fueled further investigation into the principles underlying screw mechanisms.

Advancements Beyond the Renaissance
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While the Renaissance provided a vital impetus for the development of screw thread technology, it was during the subsequent centuries that many of the most significant advancements occurred. The groundwork laid by Renaissance thinkers and tinkerers paved the way for figures such as Henry Maudslay in the 18th century, who developed the first precision screw-cutting lathe, marking a milestone in the standardization of screw threads.

The Age of Enlightenment and Beyond

Picture
Antoine Thiout, a distinguished 18th-century French clockmaker, authored a seminal work in the field of horology that became a widely acclaimed reference throughout the late 1700s. His book, "Traité de l’horlogerie mechanique et Pratique," first published in 1741, offers a comprehensive overview of watch and clock components, the use of compasses, mechanics, pendulum construction, among other topics. What sets this treatise apart are the exceptional, fold-out illustrations it contains—detailed depictions of watch and clock parts along with guided instructions for crafting timepieces. These intricate plates not only embellish the work but also provide invaluable insight into the art and science of horology during that era.
The Age of Enlightenment, a period distinguished by a fervent quest for knowledge and understanding, significantly impacted the development of mechanical engineering and manufacturing technologies. Two figures stand out for their contributions to the evolution of screw threads: Antoine Thiout and Ernst Lowenhertz. Their work not only represented breakthroughs in precision machining but also laid foundational principles for the standardization of mechanical components, which are still influential today.

Antoine Thiout's Innovations with the Lead Screw
Antoine Thiout, a French horologist and inventor, made a monumental advancement in the mid-18th century by introducing the lead screw into the lathe. This innovation was more than just a technical update; it was a paradigm shift in the manufacture of screw threads, enabling the creation of accurate and repeatable threads for the first time in history.

The Mechanism and Impact
The lead screw, essentially a long screw that controls the movement of the tool carriage in synchronization with the spindle, allowed for precise control over the cutting tool's movement along the axis of the workpiece. This meant that machinists could produce threads of consistent pitch and depth, a crucial requirement for the burgeoning fields of scientific instrumentation and mechanical engineering.

Thiout's introduction of the lead screw enabled not just precision but also versatility in manufacturing, as it allowed for the production of a wide range of thread profiles and sizes. This capability was instrumental in the production of scientific instruments, where precision and reliability were paramount. The lead screw mechanism became a standard component of lathes, underpinning the development of modern machining and manufacturing processes.

​Ernst Lowenhertz and the Discovery of the Optimal Thread Angle
Ernst Lowenhertz, working in Prussia in 1762, made a significant contribution to the standardization of Ernst Lowenhertz, in his groundbreaking work in Prussia in 1762, made a defining contribution to the field of mechanical engineering by identifying the optimal thread angle for screw threads to be 54° 45'. This discovery significantly advanced the standardization of screw threads, marrying strength with manufacturing efficiency in a manner previously unachieved. Lowenhertz's investigation into the optimal thread angle was not solely a matter of empirical experimentation; it was deeply rooted in theoretical analysis, notably leveraging an understanding of material stresses and Poisson's Ratio.


Integrating Poisson's Ratio in Thread Angle Determination
Poisson's Ratio, a fundamental principle that describes the ratio of transverse strain to axial strain in materials subjected to axial load, was critical to Lowenhertz's analysis. By applying this concept, Lowenhertz could more accurately predict how materials would behave under the stresses encountered by threaded joints. The selection of the 54° 45' thread angle was, therefore, not arbitrary but a calculated decision based on how materials deform under load.

Understanding material deformation is crucial in designing threads, as it affects both the strength of the threaded connection and its reliability over time. Lowenhertz's application of Poisson's Ratio allowed him to determine that a 54° 45' angle offered an optimal balance: it maximized the contact area between the threads, thereby evenly distributing the forces and minimizing the stress concentrations that lead to material failure. This insight was instrumental in improving the longevity and durability of screw threads.

The Rationale Behind the Angle
The specific angle of 54° 45' facilitated not only an enhanced load-bearing capacity but also addressed manufacturing considerations. By understanding the material stresses and applying Poisson's Ratio, Lowenhertz ensured that the threads could be produced with the technology available at the time, without compromising on strength. This balance between theoretical ideals and practical feasibility was pivotal in the widespread adoption of his thread design. Moreover, the angle made the engagement and disengagement of threads smoother, an essential feature for the efficient operation of machinery.

The Legacy of Lowenhertz's Work
Lowenhertz's innovative use of theoretical principles like Poisson's Ratio in the practical problem of determining the optimal thread angle was a hallmark of the Age of Enlightenment's approach to scientific inquiry and mechanical design. His work laid the foundation for further standardization in screw thread design, emphasizing the critical role of material science and geometric considerations in engineering.

​The Legacy of Thiout and Lowenhertz
The contributions of Ernst Lowenhertz, alongside those of contemporaries like Antoine Thiout, marked a significant leap forward in the precision and reliability of mechanical systems. Their work exemplifies the Enlightenment's spirit of exploration and rationality, showcasing how a deep understanding of fundamental scientific principles can drive technological progress and innovation. The principles established by Lowenhertz continue to influence modern manufacturing and engineering, underscoring the lasting impact of his contributions to the development of mechanical technology.

Their contributions exemplify the Enlightenment's spirit of inquiry and improvement, demonstrating how thoughtful innovation can lead to advancements with lasting impact. The principles they established continue to underpin modern manufacturing and engineering, reflecting the enduring significance of their work in the development of mechanical technology.

The Gribeauval System: Revolutionizing Military Engineering

Gribeauval system field artillery gun barrels are shown. From left to right, they are 12-, 8-, and 4-pounders
Gribeauval system field artillery gun barrels are shown. From left to right, they are 12-, 8-, and 4-pounders
Jean-Baptiste Vaquette de Gribeauval, an esteemed French artillery officer and engineer, revolutionized artillery design and manufacturing in the late 18th century with his Gribeauval system. This innovative approach was born out of Gribeauval's experience in military engineering, including significant exposure to the advanced yet varied artillery practices of the Austrian army, juxtaposed with the inefficiencies he observed within the French military's artillery.

Rethinking Artillery Production
The crux of the Gribeauval system lay in its radical standardization of the manufacture and assembly of artillery equipment. Prior to this, French artillery components were produced in a bewildering array of sizes and designs, making maintenance and resupply overly complex and inefficient. Gribeauval's vision was to unify these disparate elements by standardizing the dimensions and designs of cannons, carriages, and ancillary components. This initiative aimed not only to enhance the mobility and efficiency of the French artillery but also to significantly ease maintenance efforts.

A Pioneering Approach to Screw Threads
A particularly transformative aspect of Gribeauval's system was its standardization of screw threads. Until then, the lack of uniformity in thread design across various components often led to compatibility issues, severely hampering the assembly and repair of artillery pieces. Gribeauval recognized that standardizing screw threads would facilitate the interchangeability of parts, a concept that was revolutionary at the time.

By implementing a uniform thread system, Gribeauval ensured that all threaded components—ranging from the screws securing cannon barrels to the carriages, to the fastenings used in assembling the gun's aiming mechanisms—could be manufactured to a common standard. This not only streamlined the production process but also significantly reduced the logistical burden of maintaining and repairing artillery in the field. The ability to easily replace or interchange parts without the need for custom-fitting was a monumental step forward in military engineering.

Legacy and Impact on Industrial Manufacturing
The Gribeauval system's introduction of interchangeable parts, underpinned by the standardization of screw threads, had a profound impact beyond military applications. It demonstrated the practicality and efficiency of mass production techniques, paving the way for their adoption across various sectors of industry. The principles of standardization and interchangeability laid down by Gribeauval became cornerstones of the Industrial Revolution, fundamentally changing manufacturing processes around the world.

The standardization of screw threads, in particular, emerged as a critical factor in the evolution of engineering and manufacturing, allowing for the widespread adoption of machinery and equipment with interchangeable components. This not only enhanced productivity and innovation within industries but also significantly reduced costs and improved the reliability of mechanical systems.
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In summary, Jean-Baptiste Vaquette de Gribeauval's system was a groundbreaking achievement that extended well beyond the realm of military engineering, influencing the development of manufacturing and industrial practices through its pioneering standardization of screw threads and the concept of interchangeable parts. This legacy of Gribeauval's innovation continues to underpin modern engineering and manufacturing to this day.

Eli Whitney and Industrial Espionage

First milling machine, Eli Whitney, about 1820
First milling machine, Eli Whitney, about 1820
Eli Whitney, an American inventor best known for his invention of the cotton gin, is also a figure of intrigue in the history of industrial innovation, particularly for his alleged role in industrial espionage related to the development of screw threads.

The Spy Story
According to popular but not well-documented accounts, Whitney, in the late 18th century, undertook a secretive mission to England with the aim of learning British manufacturing secrets. Britain was the world leader in industrial processes at the time, and Whitney was keen to understand the advanced techniques employed in British factories. The story goes that Whitney managed to gain access to a British factory where he observed the use of taps and dies for threading, a technology that was then not widely used in the United States.

Whitney is said to have either memorized or clandestinely obtained drawings and specifications for the tap and die set, and upon his return to the United States, he reproduced the tools. This act of espionage, whether entirely factual or embellished, highlights the lengths to which individuals and nations would go to secure technological advances during the industrial revolution.

Impact on Whitney's Later Inventions
The knowledge and tools Whitney acquired, according to the tale, played a crucial role in his future inventions, particularly in the development of the cotton gin and his contributions to the concept of interchangeable parts in manufacturing firearms. The precise threading tools enabled Whitney to produce components to exacting standards, facilitating the assembly and repair of machines with interchangeable parts.
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Whitney's actions, and the broader adoption of standardized screw threads and interchangeable parts, had a lasting impact on manufacturing. The ability to produce standardized, interchangeable components revolutionized production processes, making them more efficient and significantly lowering costs. Whitney's contributions to this field underscore the critical role of innovation—and sometimes, espionage—in driving technological progress.

The Advent of Standards

Whitworth thread form
Whitworth thread form
In the mid-19th century, Joseph Whitworth introduced a seminal development in the standardization of screw threads that would have a profound impact on manufacturing and engineering. Building on the work of predecessors like Ernst Lowenhertz, Whitworth made a critical adjustment to the thread angle, simplifying it from the precise 54° 45' determined by Lowenhertz to a more practical 55°. The Whitworth thread system was adopted by the British railways in 1841, and soon other industries followed suit.

This adjustment, though seemingly minor, played a significant role in the advancement of thread standardization, leading to the establishment of the British Standard Whitworth (BSW) system, which became a cornerstone of industrial standards through the 20th and into the 21st century.

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Rationalization of the Thread Angle
Whitworth's decision to adjust the thread angle to 55° was driven by considerations of manufacturing simplicity and efficiency. The slight increase in angle simplified the tooling required for thread cutting, making the production process more straightforward and less costly. This rationalization was crucial at a time when manufacturing industries were scaling up and seeking efficiencies in mass production. The 55° angle maintained the mechanical advantages of Lowenhertz's design, such as strength and ease of engagement, while streamlining manufacturing processes.
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Importance and Impact on Manufacturing
Whitworth's simplification was important for several reasons. First, it demonstrated the value of standardization in engineering components, showing that a balance could be struck between optimal mechanical design and manufacturability. Second, by standardizing the thread angle, Whitworth facilitated the widespread adoption of interchangeable parts, a concept that was revolutionary for industrial manufacturing. This interchangeability was a key factor in the success of the industrial revolution, enabling the mass production of goods with consistent quality and compatibility.

Foundation of the BSW Standards
The adoption of Whitworth's 55° thread angle laid the groundwork for the British Standard Whitworth (BSW) system, one of the first standardized systems for screw threads. The BSW standards provided a uniform framework for the dimensions and thread angles of screws, bolts, and nuts, making it easier for industries across Britain and eventually the world to ensure compatibility and reliability of mechanical components. This standardization was instrumental in accelerating industrial development, facilitating the growth of engineering disciplines, and promoting international trade and cooperation.

Legacy Through the 20th and 21st Century
The legacy of Whitworth's standardization efforts, particularly the transition to a 55° thread angle, extends far beyond his time. The principles of the BSW system influenced subsequent standards, including the Unified Thread Standard (UTS) and the International Organization for Standardization (ISO) metric thread standards. These later standards have continued to evolve, but they all share a common lineage that traces back to Whitworth's pioneering work. His contributions have enabled industries to achieve higher levels of precision, efficiency, and quality in manufacturing, underpinning the development of modern technology and infrastructure.
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Whitworth's adjustment of the thread angle to 55° and the establishment of the BSW standards were pivotal in shaping the landscape of manufacturing and engineering. By prioritizing both practicality in production and the need for mechanical efficiency, Whitworth set a precedent for standardization that has supported technological advancement and global industrialization for over a century.

Whitworth threads, which featured radiused roots, exhibit significantly enhanced fatigue strength and were less prone to cracking in the sharp corners at the roots of Vee Form threads. However, the complexity of manufacturing tools for cutting these rounded surfaces is greater compared to those used for creating the National Standard's flattened roots and crests which we will talk about next. 

Specialized Thread Standards​
In addition to the more widely adopted thread standards, there exist several specialized threads catering to specific industry needs. For instance, both Swiss Thury and British Association Threads feature a unique 47.5° thread angle, distinct from the more common angles used in general manufacturing.

oth of these standards are optimized for precision applications like watchmaking, instrumentation, and micro-engineering. Their fine pitch facilitates exact adjustments and strong connections, especially  in small diameter, thin-walled components used in delicate and precise assemblies.  They also offers a good balance between tensile strength and minimal cross-sectional area, which is particularly beneficial for small diameter fasteners

The "Jewelers Thread," which boasts an 80
° thread angle, continues to be utilized in the craftsmanship of precious metal items made from silver, gold, and platinum.

The advantage of using  of using a Jewelers Thread lies in its ability to provide a greater surface area for contact between the threads. This increased contact area enhances the grip and strength of the connection without exerting excessive pressure on the softer, more malleable materials. Precious metals are known for their ductility and softness, which can make them prone to damage or deformation under stress. The wider thread angle of the Jewelers Thread helps distribute the force more evenly across the threads, reducing the risk of stripping or damaging the thread in these valuable materials.

These less common threads underscore the diversity in thread design, tailored to meet the precise requirements of various materials and applications.

World War I and the ABC Standards

World War I was a catalyst for significant advancements in industrial standardization, particularly in the domain of screw thread standards. The war's demands for rapid production and repair of military machinery and equipment underscored the critical need for uniformity in manufacturing processes among the Allies. This period saw the emergence of the American British Canadian (ABC) Council of Industry, which played a pivotal role in adopting a unified approach to screw thread standardization, notably the adoption of a 60-degree thread angle.

The groundwork for screw thread norms in the United States was laid by William Sellers in 1864, who proposed a 60-degree thread angle among other specifications, later known as the Sellers thread. The Franklin Institute of Philadelphia backed this proposal, and by 1868, it was approved for use in the U.S. naval service. 
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By 1871, the railway industry adopted it for locomotives and cars, and its widespread acceptance across various sectors soon followed. 

The Need for Screw Thread Standards
The WWI war effort required the mass production of weapons, vehicles, and other military hardware at an unprecedented scale. The lack of standardized screw threads posed a significant challenge, as components manufactured in one country often did not fit machinery produced in another.

​This incompatibility led to delays in manufacturing and repair, directly impacting the effectiveness and efficiency of the war effort. Standardized screw threads were necessary to ensure that parts could be produced, exchanged, and repaired quickly and efficiently across different nations' industries.

Graphic representation of formulas for the pitches of threads of screw bolts
Graphic representation of formulas for the pitches of threads of screw bolts
Adoption of a 60° Thread Angle
The decision to adopt a 60° thread angle over the previously common 55° angle which was the Whitworth standard, was driven by the need for a more simplified, versatile, and robust standard that could be easily adopted by manufacturers across different countries.

​The 60° angle was found to offer a good balance between strength and ease of manufacture, making it suitable for the diverse range of applications encountered in military hardware. This angle facilitated the creation of threads that were both strong and easy to engage and disengage, which was crucial for the maintenance and repair of equipment in the field.


The ABC Simple Fit Guide and Standardized Pitches
​The ABC Council further introduced a simple fit guide and standardized pitches for each screw diameter. It used the the rounded root form of the Whitworth to improve fatigue performance and the 60° flank angle and flat crests from Sellers, therby streamlining the production and interchangeability of threaded components. This standardization was essential for accelerating production times, reducing waste, and ensuring that components from different suppliers could be used interchangeably without the need for custom fitting.


The Unified National Thread Standard and Post-War Developments

The basic profile of all UTS threads is the same as that of all ISO metric screw threads. Only the commonly used values for Dmaj and P differ between the two standards
The basic profile of all UTS threads is the same as that of all ISO metric screw threads. Only the commonly used values for Dmaj and P differ between the two standards
The establishment of the Unified National Thread Standard (UNTS) and the adoption of metric standards post-World War II represent pivotal moments in the quest for global uniformity in manufacturing. These developments, aimed at simplifying international trade and enhancing the dissemination of technology and goods, underscored the critical importance of standardized components in the industrial landscape. The journey towards this uniformity, characterized by significant milestones and strategic shifts, reflects the evolving needs of industrial efficiency and technological innovation.

From World War I to the Unified National Thread Standard
The seeds for the Unified National Thread Standard were sown during the exigencies of World War I, where the American British Canadian (ABC) Council's efforts to standardize screw threads highlighted the strategic advantages of interoperability and manufacturing efficiency. This period underscored the necessity for a unified approach to component manufacturing, setting the stage for the development of a comprehensive national standard in the subsequent decades.

In the 1920s, under the auspices of the American Standards Association (ASA), the principles established by the ABC Council during the war years were refined and expanded, culminating in the creation of the Unified National Thread Standard. This initiative was driven by the burgeoning demand for industrial efficiency and the interoperability of components, especially within the rapidly growing automotive and manufacturing sectors in the United States.

The Formation of ANSI and the Introduction of UNC and UNF
The geopolitical and technological landscape of the late 1950s, particularly marked by the Soviet Union's launch of Sputnik, prompted a reassessment of the United States' technological and industrial strategies. This event, known as the Sputnik crisis, catalyzed a renewed focus on technological and industrial competitiveness. In response, the American Standards Association was reorganized into the American National Standards Institute (ANSI) in 1958, a move that underscored the burgeoning importance of standardization in bolstering national security and fostering technological advancement.

Amidst this backdrop of strategic realignment, the thread standards underwent further refinement, leading to the differentiation into Unified National Coarse (UNC) and Unified National Fine (UNF) thread forms. This bifurcation was a strategic decision aimed at addressing the nuanced requirements of various industrial applications. The coarser UNC threads were designed for general applications, prioritizing ease of use and manufacturing. Conversely, the finer UNF threads were tailored for applications demanding higher tensile strength and precision, showcasing an ongoing evolution and specialization in screw thread technology to meet specific engineering needs.


The Rationale for UNC and UNF Threads

Replica of Sputnik 1 in the Museum of Space and Missile Technology (Saint Petersburg)
Replica of Sputnik 1 in the Museum of Space and Missile Technology (Saint Petersburg)
The Formation of ANSI and the Introduction of UNC and UNF
The launch of Sputnik by the Soviet Union in 1957 triggered the Sputnik crisis, leading to a renewed emphasis on technological and industrial competitiveness in the United States. In response, the American Standards Association was reorganized into the American National Standards Institute (ANSI) in 1958, reinforcing the importance of standards in national security and technological advancement.

This period also saw the rationalization of thread standards into two primary forms: the Unified National Coarse (UNC) and Unified National Fine (UNF) thread forms. The rationale behind creating these two standards was to cater to the diverse needs of various applications.

UNC threads, being coarser, were ideal for general applications where ease of use and manufacturing were prioritized. Coarse-threaded bolts, cut deeper into materials, have a smaller root diameter, making them less strong but suitable for gripping soft materials like cast iron and aluminum in rougher applications. In contrast,

In contrast, UNF fine-threaded fasteners boast superior strength and vibration resistance, fitting for harder materials. Automotive and aircraft studs exemplify this duality, with coarse threads at one end for better grip in softer engine metals and fine threads at the other for stronger hold in steel nuts.
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Coarse-threaded bolts, cut deeper into materials, have a smaller root diameter, making them less strong but suitable for gripping soft materials like cast iron and aluminum in rougher applications. In contrast, fine-threaded fasteners boast superior strength and vibration resistance, fitting for harder materials. Automotive and aircraft studs exemplify this duality, with coarse threads at one end for better grip in softer engine metals and fine threads at the other for stronger hold in steel nuts.

The creation of UNC and UNF standards was a strategic response to the varied demands of different applications, with UNC threads catering to ease of use in general applications, and UNF threads providing the required strength and precision for more demanding tasks.

The Future Standards of Screw Threads

Volume Graphics develops leading software for the analysis and visualization of industrial 3D computed tomography data.
image source via Volume Graphics. Developers of leading software for the analysis and visualization of industrial 3D computed tomography data. Click on the image to link to their website
The landscape of screw thread technology is poised for transformative advancements, significantly influenced by progress in materials science, manufacturing techniques, digital technologies, and the specific needs of niche applications. These developments promise to redefine the capabilities and applications of screw threads across various industries.

Here are some areas where we can expect to see significant progress:
  1. Advanced Materials: The use of new materials, such as high-strength alloys, polymers, and composites, will drive the development of screw threads that can withstand extreme conditions such as higher temperatures, corrosive environments, and greater mechanical loads. This could lead to threads with improved longevity, reliability, and performance in sectors like aerospace, automotive, and medical devices.
  2. Additive Manufacturing: With the rise of 3D printing, there's potential for more complex thread designs that are optimized for specific functions, such as self-tapping screws for improved load distribution or threads that enhance sealing capabilities. Additive manufacturing allows for the production of geometries that are difficult or impossible to achieve with traditional machining processes.
  3. Nanotechnology: At the micro and nano scale, screw threads could be used in precision devices and instruments. Nanotechnology could lead to the development of micro-fasteners for use in electronics, microfluidics, and medical implants, requiring precise control over thread geometry at the micro-scale.
  4. Smart Threads: Incorporating sensors or smart materials into threads could enable the monitoring of bolted connections in real-time for stress, temperature, or vibration. This could be particularly useful in critical infrastructure, machinery, and aerospace applications, where maintaining the integrity of fasteners is crucial.
  5. Sustainability: As industries focus more on sustainability, there will be a push towards designing screw threads that are easier to recycle or manufactured from recycled materials. Additionally, developments might focus on reducing material usage without compromising strength or using materials that have a lower environmental impact.
  6. Standardization for Global Markets: As global manufacturing continues to grow, there will be an increasing need for international standardization of thread forms to facilitate compatibility and interoperability across borders. This could involve the harmonization of existing standards or the development of new global standards to address emerging technologies and materials.
  7. Hybrid Threads: Innovations may include hybrid thread forms that combine the best features of existing thread types to offer superior performance in specific applications, such as enhanced resistance to loosening under vibration or improved load distribution to minimize material fatigue.

These anticipated advancements in screw thread technology are driven by the imperative for higher performance, greater efficiency, and more sustainable manufacturing practices. As industries evolve, the requirements for threaded fasteners will also advance, spurring ongoing innovation in this fundamental aspect of mechanical design.

​The detailed history of screw threads from ancient innovations to contemporary standards reveals a continuous thread of ingenuity and the pursuit of precision and efficiency. Each period brought forth advancements that built upon previous knowledge, reflecting humanity's relentless drive to improve and standardize the fundamental components that underpin mechanical and engineering achievements.


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What is "Class of Fit" for a Cutting Tap?

10/17/2023

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written, compiled and edited by Bernard Martin
What does Class of Fit for a Cutting Tap mean
The basic profile of all UTS threads is the same as that of all ISO metric screw threads. Only the commonly used values for Dmaj and P differ between the two standards.
Class of fit for a cutting tap refers to the specific tolerance or fit that is desired between the threads of the tap and the threads of the hole it is being used to create. In other words, it defines how tightly or loosely the threads should mesh together.

The class of fit is typically expressed using a combination of letters and numbers. The most commonly used standards for class of fit are the Unified Thread Standard (UTS) and the ISO metric thread standard. In the UTS, the class of fit is denoted by a combination of a letter and a number, such as 2B, 3A, etc. In the ISO metric thread standard, it is represented by a combination of a letter and a number, such as 6g, 4h, etc.

For cutting taps, the class of fit is usually specified based on the intended application and the level of precision required. The class of fit can affect factors like the ease of assembly, the strength of the threaded connection, and the ability to engage the threads smoothly during tapping.

A classification system exists for ease of manufacture and interchangeability of fabricated threaded items. Most, but certainly not all, threaded items are made to a UTS classification standard. This system is analogous to the fits used with assembled parts.
  • Class 1 threads are loose fit, intended for ease of assembly or use in a dirty environment.
  • Class 2 threads are free fit, and the most common. They are designed to maximize strength considering typical machine shop capability and machine practice.
  • Class 3 threads are medium fit, still quite common and used for closer tolerances on high quality work.
  • Class 4 threads previously designated a close fit for even tighter tolerances, but this classification is now obsolete.
  • Class 5 fit is an interference thread, requiring the use of a wrench for turning. These can be seen in applications like spring shackles on an automobile.

The letter suffix "A" or "B" denotes whether the threads are external or internal, respectively. Classes 1A, 2A, 3A apply to external threads; Classes 1B, 2B, 3B apply to internal threads

Here are some common classes of fit for cutting taps:
  1. Class 2B (UTS) or 6H (ISO metric): This is a standard fit for most general-purpose applications. It provides a balance between ease of assembly and thread engagement.
  2. Class 3B (UTS) or 6HX (ISO metric): This is a tighter fit than Class 2B or 6H and is used when a higher level of thread precision and engagement is required.
  3. Class 2A (UTS) or 6g (ISO metric): This is a loose fit that is often used for applications where ease of assembly and disassembly are important, such as with interchangeable parts.
  4. Class 3A (UTS) or 6HX (ISO metric): This is a tighter fit than Class 2A or 6g and is used in applications where a higher level of precision is required.
The choice of class of fit should be made based on the specific requirements of the project, taking into consideration factors like material type, thread size, intended use, and the desired level of thread engagement. It's important to consult relevant standards and guidelines to ensure that the chosen class of fit is appropriate for the application.
​
The standard designation for a UTS thread is a number indicating the nominal (major) diameter of the thread, followed by the pitch measured in threads per inch. For diameters smaller than 1⁄4 inch, the diameter is indicated by an integer number defined in the standard; for all other diameters, the inch figure is given.

This number pair is optionally followed by the letters UNC, UNF or UNEF (Unified) if the diameter-pitch combination is from the coarse, fine, or extra fineseries, and may also be followed by a tolerance class.
Example: #6-32 UNC 2B (major diameter: 0.1380 inch, pitch: 32 tpi)
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Detailed Guide to Roll Taps

4/18/2023

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Technical article courtesy of  Regal Cutting Tools
​
Most craftspeople will agree that whenever an internal thread can be made with a roll form tap, this is the tool that should be used for the job. Roll taps, also known as form taps, hold distinct advantages over cut taps. Roll tap advantages are inherent in the way they create the threads.

As the names suggest, these taps form the threads by rolling and deforming the material inside the hole. They push the metal out of the way to create the thread roots and base. Cut taps, also true to their name, carve metal away from inside the hole, ejecting chips as they go.

Reasons to Use Roll Form Taps

Roll taps are a great option when considering workmanship and price point. First, roll taps are chipless. Because they do not remove material from the hole, form taps generate no chips that must be removed. This carries several advantages:

  • Tool Life – Cut taps have flutes cut into them through which chips migrate up and out of the hole during threading. Flutes take away the taps’ bulk and rigidity, weakening them and making them more susceptible to wear and breakage.

  • Efficiency – Flushing chips from a blind hole and disposing of them takes time. Roll taps eliminate this wasted time so machinists can thread more holes in the same amount of time. Roll taps’ strength also permits their use at higher feeds and speeds, increasing their efficiency even more.

  • Thread Quality – Forming threads rather than cutting them creates more precise pitch diameters and surface finishes. Just as important, rolled threads are stronger than cut threads because the metal grains are deformed along the thread contours.

  • Speed – Roll form taps should be run at 1-1/2 to 2 times the speed of a cut thread tap for a given material. The forming action creates heat and can “work harden” the material being formed. It is a good practice to form the thread and reverse out of the hole as quickly as possible.
Regal Roll Form MetFlo Taps
Regal MetFlo Taps

When Not to Use Roll Taps

While an excellent choice for most applications, there are a few situations that do not lend themselves to roll tapping including:
  • Threading a through-hole – Form taps may deform the exit hole, which will necessitate a second, time-consuming step to repair. Spiral-point cut taps are the best option for such a job. They push chips ahead of the cutting edges, keeping flutes clean. The chips fall harmlessly out the exit hole as the tap breaks through.

  • You’re threading a big hole – Thread-cutting taps require less horsepower than thread-forming taps. Cutting large holes with a form tap requires twice or three times as much torque as with cut taps, which can take its toll when threading large internal surfaces.
​
  • The workpiece is hard –Form taps are suitable only for soft and malleable metals such as soft steel, some stainless steels, aluminum, copper, brass, and lead. Typically, the material to be formed should be less than 32Rc in hardness.
​

Types of Roll Taps

Roll taps are engineered and manufactured in two main styles to match the type of hole and fastener to be used. Bottoming roll taps feature little to no taper on their end threads. This allows full thread production to the very bottom of the hole.

The bottom 3 to 5 threads on a plug tap are tapered to allow the tap to gradually begin deforming the hole material, creating less stress on the tool and giving the full threading edges a base from which to work.
 
Regal Cutting Tools has built a reputation for high quality taps and other metalworking tools and an uncompromising commitment to customer service. Regal manufactures a full line of roll taps to suit any application. Regal can even engineer custom taps quickly and affordably. To learn more about Regal’s taps and learn which products are best suited for your workflow, contact our team today.
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Fast Change Tooling System Increases Spindle Uptime

6/14/2022

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Appears in Print at Production Machining as: 'A Swift Tool Change for Swiss-Type Machines'
​
​This coolant-through tooling system replacement for the gang plate on a Swiss-type machine can save hours of spindle downtime per day as well as increase tool life and enhance chip control.

by LORI BECKMAN Senior Editor Production Machining
​
While servicing the tools on a traditional platen on a sliding headstock lathe, it can take 10 minutes or more to index one insert. While indexing the tools, coolant spigots can get knocked loose by an operator and can cost a machine shop tool life and time. Once the inserts are indexed, it can take several starts and stops of the spindle for the operator to see if the coolant stream is being directed to where it needs to be.
​
To optimize this tool change process, Arno-Werkzeuge USA LLC has developed a coolant-through fast change tooling system that eliminates the high-pressure coolant lines in a Swiss-type’s compact workzone.

​The company says it also significantly decreases tool change downtime as well as setup time from hours to minutes while offering accurate repeatability.

​These advantages not only increase finished part output but also save thousands of dollars per spindle per year, according to the company.
Arno’s Fast Change (AFC) tooling system consists of a gang plate that holds split-shank, coolant-through turning tools, parting tools and grooving tools. Photo Credits: Arno USA
Arno’s Fast Change (AFC) tooling system consists of a gang plate that holds split-shank, coolant-through turning tools, parting tools and grooving tools. Photo Credits: Arno USA
Arno’s Fast Change (AFC) tooling system consists of a gang plate that holds split-shank, coolant-through turning tools, parting tools and grooving tools. Designed like a manifold, the coolant is rerouted through the gang plate to the tools. The UN-style slot in the fixed stop picks up the coolant and runs it through the pipette to the front end where the coolant goes directly to the cutting edge. The AFC system can supply coolant to one port that supports all the tooling positions, or it can supply two ports and divide the tooling positions with the needle valve.

The tooling system only needs to be plumbed once and, according to the company, after that, a high-pressure coolant line should not need to be touched again. With proper setup, the high-pressure lines are moved behind the machine guards, creating a clean machining environment. This enables operators to complete safer routine maintenance. Also, the AFC’s low-profile clamps do not collect as many chips compared with a typical clamping system.

When replacing a split-shank tool, the operator simply loosens two clamps to remove the cutting head and then replaces it with a new one, the company says.

Simple, Quick Functionality

A Time and Money Saver

Using the AFC system, Arno reports that it takes 17 seconds to change a tool, a vast improvement to the typical 7 to 10 minutes it can take using a traditional gang plate. The conventional method might take five minutes to change a tool, a minute to touch the tool off and another minute to adjust the spigot, for instance.
ARNO Fast Change Tooling System
Arno’s Fast Change (AFC) tooling system consists of a gang plate that holds split-shank, coolant-through turning tools, parting tools and grooving tools. Photo Credits: Arno USA
“Then, when you scale that up to a three-shift operation, you will change tools in all five stations twice per shift,” explains Keith Stroup, business development manager at Arno.

“So, 10 tool changes per shift on all five stations twice per shift equals 30 times that spindle will be idle at seven minutes each.”

He figures that is three and half hours, or nearly half a shift of idle time, just to service the tools in that traditional manifold and spigot platen.

​“Three and a half hours every 24-hour cycle equates to $70,000 per year of spindle downtime to service the tooling in that gang plate,” he adds.
In comparison, when an operator is working with the AFC system, retouch is not necessary because the tool will repeat within plus or minus a thousandth of the previous tool positions. There is also no need to factor in time for readjusting coolant lines because the new system is a true, coolant-through system.

It is also not necessary to factor in the clearing away of chips because those surfaces have mostly been eliminated with the smooth AFC design, according to Stroup. Therefore, the 17-second tool change time is the only time to factor in.

​But, for a real-world example, he increases the time to one minute to consider a distracted operator that might use extra seconds
Arno Cost Calculator
These charts show estimates of cost savings using Arno Fast Change tooling system versus the standard monoblock tool system. Arno says users can gain $60,000 per year by using its Fast Change system.

Although there are still 30 idle times per day, there are now only 30 minutes of downtime per day instead of 210 minutes using the traditional gang plate. “That only costs $10,000 per year, which means you’ve just made $60,000 a year on that one spindle by adopting the AFC system,” Stroup says.
​

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Need Carbide Fractional and Metric Taps? Allen Benjamin Has You Covered

1/13/2021

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Almost a year ago, Allen Benjamin, which has been a part of North American Tool,  was purchased by GWS Tool Group. GWS Tool Group is a US-based, vertically integrated manufacturer of highly engineered custom, standard, and modified standard cutting tools, primarily servicing the aerospace and defense, power generation, automotive and medical sectors. GWS Tool Group has acquired multiple businesses in the course of its growth which now serves as the respective manufacturing divisions for the Company.  

Just because there is a new owner, doesn't mean that the quality of an Allen Benjamin Tap has changed! 

If you’re in the market for high tensile strength carbide taps and metric taps, we can assure you that you’re in the right place. Not only is Allen Benjamin a leading supplier of the industry’s most durable, longest lasting carbide taps, we offer our customers the convenience of ordering online. In this day and age, we believe that quick access and top-notch customer services are critical.

In today’s post, we’re going to look at why it is beneficial to order your carbide taps from Allen Benjamin.

Quality
Allen Benjamin carbide taps are highly efficient when tapping abrasive metals such as aluminum, non-ferrous metals, and exotic materials. With a much higher tensile strength than standard taps, their high-quality carbide taps can withstand the rigorous demands of your application.

Selection
Allen Benjamin offers a staggering range      of carbide taps, metric taps, HSSE taps, tapping fluid, extensions, and more. If it’s taps that you are looking for, you can be confident that they’ve got them and have them ready for delivery.

Service
Allen Benjamin guarantees that all of their products will be the absolute best quality, within standard tolerances and dimensions, and consistent with application specifications. If their goods don’t meet your needs, you can contact us for a return authorization.

At Allen Benjamin, they take pride in offering the industry’s best taps. But, more importantly, they aim to provide our customers with access to a simpler, faster way to order their operation’s critical parts, supplies, and components.

If you’ve been searching for a supplier that will meet your needs and rise to meet your challenges contact us today!

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Understanding Tap "Relief"

1/19/2020

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Have you ever had a tapping job that was so troublesome that it caused heartburn or acid indigestion due to broken taps, bad finish, short tap life, over or undersized threads, etc.?

One way of avoiding or alleviating such a condition is accomplished with the use of a tap feature called “relief”. The definition of “relief” according to Marian Webster, is removal or lightening of something oppressive, painful, or distressing.

For a tap, “relief” is the reducing of surface contact between the tap/tap feature and the part being tapped. Surface contact generates unwanted heat causing the issues mentioned above. Depending on the tap feature, relief is applied in a direction that is, radially, around the tap, or axially, along the axis of the tap.

All taps require a minimum number of features to have relief for it to cut, other reliefs are applied when the tapping application requires it. There are always tradeoffs when designing a tap, if a relief is applied or it’s amount is greater than necessary, it can cause the tap to run free or loose to a point it will cause heartburn or acid indigestion by producing issues mentioned above.
​
Relieved features that are always necessary on a tap are:
               
Chamfer, the tapered threads at the front of the tap. The crests or major diameter of the chamfered threads are radially relieved from the cutting edge to the heel of the land. Without this relief it would be like cutting a tomato with the non-sharp side of a knife, you can imagine the results of that. When looking at a taps chamfer, relief results in the crest width being wider at the cutting edge and narrowing towards the heel;
Tap Chamfer
Cut Tap Cutting-Edge Heel
Back Taper, a slight gradual reduction of the taps thread form including it’s major, pitch and minor diameters. It starts at the chamfered end of the tap and continues axially for the length of thread towards the shank end.

A typical diameter reduction amount for a standard tap is 0.005/0.0010 per inch. This amount may be increased for specially designed taps used for tapping materials that close in excessively on the tap.

The chamfer threads, as well as the first full thread of the tap, do the cutting and the balance of the non-chamfered, non-relieved threads, go for the ride helping guide the tap. Back taper prevents surface contact of the non-chamfered threads with the part material.
​
Major-Pitch Minor Diameter Tap
Additional features that can be relieved

Thread Relief, a radial reduction of the taps major and pitch diameters from the cutting edge to the heel. Relieving of the pitch diameter results in the minor diameter being relieved as well due to the manufacturing process whereas the major diameter is relieved separately. The application of the major or pitch diameter relief is normally applied separately but both can be done in combination. Relief of pitch diameter is the most common followed by the major diameter. Thread relief is applied when Back Taper alone is not enough to prevent surface contact when tapping materials that close in and squeezes the tap like stainless steel. The rate of reduction from the cutting edge to the heel is based on the material being tapped and, in some cases, the tapping application.

There are two common types of Thread Reliefs:
  • Eccentric, a radial relief in the thread form starting at the cutting edge and continuing to the heel.
  • Con-Eccentric, Radial relief in the thread form starting back of a concentric margin.
Thread-Relief-Eccentric diagram
Tap Thread Con-eccentric-Relief
The reliefs we have discussed so far are applied during the tap manufacturing and other than the chamfer relief cannot be added or changed. If you are in a bind and must ship parts but can’t wait for us to design, manufacture and ship the appropriate tap, there are additional types of relief that can be applied that may work in a pinch. Sometimes referred to as a poor man’s relief, something you may be capable of doing in your shop without too much trouble to get you through a quick job, or until properly designed tools arrive.
Tap Diagram Flatted-Grooved-Heel land
The application of relief types and amounts are dependent on many factors such as material properties being tapped, style and size of tap, how the tap is being used (hand, machine, etc.) and application requirements, etc. By providing us with as much information about your tapping application, it will enable our engineers to design a tap with the proper relief. This will help alleviate troublesome heartburn or acid indigestion.
​
Edit January 2024: Changed banner image
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The Dümmel Minimill-System for ID Grooving and Threading

11/12/2019

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The Dümmel Minimill-System with three or six cutting edges is the next big thing for ultra groove milling and threading machining from 0mm to a 32mm bore diameter.

The indexable carbide heads are screwed on with three ribs coupling. This guarantees the best possible rotation and repeatable accuracy. A large selection of standard inserts as well as toolholders from steel and carbide are available from stock.

With six cutting tools available, there's sure to be one that you can use to generate higher feed rates, longer tool life with higher stock removal rates.

The six cutting edged Minimill-system is also available with an anti-vibration carbide toolholder or a steel tool holder.
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Calculating "Before Plate" Internal Screw Thread "H" Limits

10/30/2019

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North American Tool realizes how confusing the painstaking math is to get preplate part limits and a Tap “H” limit, but don’t worry, all you have to do is contact us with your thread information, and we will do the work. Call us at 800-USA-TAPS.

If you want to know how it's done, we’ve included the formulas for the engineer in all of us.

If you want to know how it’s done, we’ve included the formulas for the engineer in all of us.
When encountering an internal threaded hole requiring it to be plated, it normally needs to be produced oversize to accommodate the plating. There are two methods for determining the correct Tap “H” limit, the “Detailed Method” and the “Simplified Method”.

The “Detailed Method” requires you to do more math, but it will also determine the before plate product limits (GO & NOGO)

The “Simplified Method” requires less math but will not provide you with the before plate product limits (GO & NOGO)
​
When the plating is applied to the properly oversized threaded hole, the required thread class (2B, 3B) or special PD (pitch diameter) will be met. The effect of plating on a 60° screw thread is a change in PD of 4 times the plating thickness (2 times on each side). That is because the plating itself is parallel to the thread flanks, and the PD is measured perpendicular to the thread axis. As an example, a .0002 plating thickness X 4 results in a PD increase of .0008 (The ratio of 4:1 is for 60° threads only, the ratio for other thread forms such as ACME, 29° is different.)

Detailed Method

Before determining the tap size (H limit), it is necessary to determine the oversize part thread limits first. Once this is achieved, the tap limit is normally position at 40% of the before plate limits.

Unfortunately, life is not always easy. The required plating thickness on the print, purchase order, etc. will be expressed in one of two ways, a “Maximum and Minimum Thickness” or a “One Value Thickness” requiring two different ways to calculate the oversize part thread limits.

Maximum and Minimum Plating Thickness
1. The Minimum part PD (pitch diameter) is larger by 4 X the Maximum plating thickness
2. The Maximum part PD (pitch diameter) is larger by 4 x the Minimum plating thickness
3. The Tap “H” = a PD that is located at 40% of the before plate limits – minimum after plate limit \ .0005 (“H” limit increment). Selecting the closes “H” limit
Example: 1/4-20 UNC-2B, plating thickness, .0002 to .0003    (1/4-20 UNC-2B after plate PD = .2175 – .2224)

1. GO Minimum before coating part PD (pitch diameter) =.2175 (after plate GO or minimum PD) + .0012 (4 X .0003 max plating thickness) = .2187
2. NOGO Maximum before coating part PD (pitch diameter) = .2224 (after plate NOGO or maximum PD) + .0008 (4 X .0002 min plating thickness)  = .2232
3. Tap ‘H” Limit 
.2232 (Maximum before coating part PD) – .2187 (Minimum before coating part PD) = .0045
.0045 X 40% = .0018
.0018 + 2187 (Minimum before coating part PD) = .2205
.2205 (before plate Tap PD) – .2175 (after plate or minimum PD) = .003
0.003 / .0005 (“H” limit increment) = H6

One Value Plating Thickness
When a “One Value Plating Thickness” is shown, we establish a maximum and minimum plating thickness values to compute the maximum and minimum before platting thread limits. This is done by assuming that the tolerance on the plating is 50% larger than the “One Value Plating Thickness.” The maximum plating thickness is 6 X, the “One Value Plating Thickness,” and the minimum plating thickness is the same as the “One Value Plating Thickness.”

1. The Minimum part PD (pitch diameter) is larger by 6 X the “One Value Plating Thickness”
2. The Maximum part PD (pitch diameter) is larger by 4 x the “One Value Plating Thickness”
3. The Tap “H” = a PD that is located at 40% of the before plate limits – minimum after plate limit \ .0005 (“H” limit increment). Selecting the closes “H” limit

Example: 1/4-20 UNC-2B, plating thickness, .0003 (1/4-20 UNC-2B after plate PD = .2175 – .2224)
​
1. GO Minimum before coating part PD (pitch diameter) =.2175 (after plate GO or minimum PD) + .0018 (6 X .0003 “One Value Plating Thickness”) = .2193
2. NOGO Maximum before coating part PD (pitch diameter) = .2224 (after plate NOGO or maximum PD) + .0012 (4 X .0003 “One Value Plating Thickness”) = .2236
3. Tap ‘H” Limit 
.2236 (Maximum before coating part PD) – .2193 (Minimum before coating part PD) = .0043
.0043 X 40% = .00172
.00172 + .2193 (Minimum before coating part PD) = .2210
.2210 (before plate Tap PD) – .2175 (after plate or minimum PD) = .0035
0.0035 / .0005 (“H” limit increment) = H7

Simplified Method

This method requires knowing what tap “H” limit that is recommended for the thread class of fit (2B 3B etc.) after plating.

Example: The recommended “H” limit for a 1/4 – 20 UNC 2B would be GH5 and for a 3B it would be GH3.

Maximum and Minimum Plating Thickness
When the plating thickness requirement is given with a maximum and minimum limit you would simply,
Example: 1/4-20 UNC-2B, plating thickness, .0002 to .0003 (1/4-20 UNC-2B after plate recommended “H” limit GH5)

One Value Plating Thickness
When the plating thickness requirement is given with a one value plating thickness limit you would simply, Multiply the plating thickness by 4 (the 60° size change ratio) to determine the PD (pitch diameter) size change in inches.

Then divide the PD size change in inches by .0005 (“H” limit increment).

The result would be the increase in “H” limit and added to the recommended “H” limit for the required after plate thread class.
​
Example: 1/4-20 UNC-2B, plating thickness, .0003 (1/4-20 UNC-2B after plate recommended “H” limit GH5)
.0003 X 4 = .0012 (PD size change in inches)
.0012 / .0005 = 2.4 (PD size change in “H” limits) rounder to the closest “H” limit = 2
Recommended “H” limit of GH5 (recommended “H” limit for Class 2B) + 2 = GH7 (pre-plate “H” limit)
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HB Rouse Carbide Cutting Tool Brand Reintroduced by Arno Werkzeuge USA

6/27/2018

3 Comments

 
Arno Werkzeuge USA has reintroduced the H.B. Rouse brand of American-made carbide cutting tools and inserts.
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Arno Werkzeuge USA has reintroduced the H.B. Rouse brand of carbide cutting tools and inserts.

Formerly sold and marketed under the Arno-Rouse name, the company has reintroduced Rouse as a standalone product offering a broad range of carbide boring bars, tools and inserts for manual turning operations.

The carbide insert turning tools have triple-sided inserts for quick change turning operations.

Triple-tip boring bars offer an improved triangular insert located within a precision-machined pocket to eliminate shifting under heavy cuts; the insert requires the simple removal of one screw for indexing.

Boring bars feature carbide inserts that provide three cutting edges instead of only one (as is common with brazed-tip tooling).

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Browne & Co., Inc.
9605 Tanager Drive
Chardon, Ohio 44024
Phone 440.285.8655
[email protected]
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