History of the Robertson Screwdriver

The Roberston screwdriver, also known as a square screwdriver, was invented in 1908 by P.L. Robertson, a native Canadian. The screwdriver presented a solution to the frequent problem users encountered with flathead screwdrivers: the driver often slipped out of place and slowed down the process of securing the fasteners. Robertson’s design depended on the corresponding square shape on the top of screws that enabled the square-shaped screwdriver to make secure contact with the screw. As the screwdriver was rotated, it was far less likely to slip out of place and the process moved a lot faster.

Once Robertson had conceived the notion of a square-headed screwdriver, he toyed with various manufacturing methods until he was able to produce screws with a square-shaped imprint on their heads. When the correctly-sized driver is inserted into a corresponding screw, the user can rortate the driver horizontally without fear of the driver slipping. Because the driver is self-centering, only one hand is needed for rotation.

Robertson patented his invention of both the square-headed screw and driver in 1909, but The Steel Company of Canada did not take kindly to his invention. Some went as far as to try to undermine his patents, but the attempts were unsuccessful. Manufacturers took to the new designs right away, and companies, such as Ford, came to depend on the screws and driver as key components in automobile production. As a result, Robertson soon produced special metal screws for Fords’ use in Model A manufacturing. Henry Ford sought a licensing arrangement with Roberston, but Robertson turned him down.

By the end of the late 1940s, Robertson’s company had grown to employ 500 people and the screws were available in three different sizes with corresponding drivers, each distinguished by one of three colors: small drivers were green, medium drivers were red, and large drivers were black. Although the design was rapidly integrated into the Canadian market and still continues to thrive today, Robertson screws and screwdrivers were much less successful in the US and are not commonly used.

Currently, there are five different Robertson screwdrivers available, with suitable screw size indicated by the color. Orange drivers (#00) are appropriate for use with screw types 1 and 2. The recess size range (the size of the corresponding square imprint on the screw) is from 1.77-1.80 mm. Yellow drivers (#0) work with screw types 3 and 4 and feature a recess size range of 2.29 to 2.31 mm. Green drivers (#1) operate with screw types 5, 6, and 7, with a recess size range of 2.82 to 2.86 mm. Red drivers function with screw types 8, 9, and 10 and have a recess size range of 3.34 to 3.38 mm. Black drivers work with the largest screws, types 12 and higher, and have a recess range of 4.81 to 4.85 mm.

Head Bolts vs Head Studs

Choosing whether to use head bolts or head studs in an automobile engine can be an important decision that affects the way a car runs. While they are both fasteners and ostensibly serve a similar function, there are a handful of differences that make studs and bolts distinct from one another. For one, bolts are usually partially or fully threaded, while studs are typically threaded on both ends and often have an unthreaded middle section of the shaft. In addition, studs do not have a head, whereas bolts always do.

When evaluating the various benefits of studs and bolts, it is helpful to keep a number of considerations in mind. Ease of engine assembly and disassembly can be a significant factor, as well as torque pressure, gasket alignment, and overall engine performance. The power and acceleration potential of an engine often dictates the type of head fastener that will be used. For example, a high-end or racing model car will have drastically different engine fastener requirements than a vehicle designed for everyday purposes.

Head Fastener Design

Comparatively speaking, head bolt design tends to focus on stability and convenience. Engine head bolts can be cold-fabricated to increase their integrity, and are often thermally treated before they are machined or have threads cut into them. They provide relatively high strength and durability, and frequently come packaged with hardened washers or nuts. Some manufacturers produce head bolts with wide flange dimensions, which reduce the need for removing the bolts or the valvetrain when conducting cylinder maintenance.

Like bolts, head studs are also thermally treated at high pressure to improve structural strength. Studs are carefully shaped to make them concentric, usually requiring a series of cuts to produce a straight, balanced component. They can be roll threaded before or after heat treatment, although post-heating roll threads provide higher mechanical strength and stress tolerance in the final product. Some head studs are designed with gasket and cylinder alignment in mind, and they are typically more expensive than the equivalent head bolt models.

Torque Efficiency

During engine assembly or maintenance, a bolt must be installed by torqueing it into place. Due to the head bolt’s design, it has to be rotated into its slot in order to engage the threads and secure it into place. This process creates both twisting force and a vertical clamping force, which means that when the cylinders within the engine’s combustion chamber begin accumulating load, the bolt will both stretch and twist. Because the bolt has to react to two different forces simultaneously, its capacity to secure the head is slightly reduced and it forms a less reliable seal in high-powered engines.

By contrast, a head stud can be tightened into place without any direct clamping force applied through the tightening. A stud can be threaded into a slot up to “finger tightness,” or the degree to which it would be tightened by hand. Afterward, the cylinder head is installed and a nut is torqued into place against the stud. The nut torque provides the clamping force, rather than the torque of the fastener itself, and the rotational force is avoided entirely. Because the stud is torqued from a relaxed state, the pressure from the nut will make it stretch only along the vertical axis without a concurrent twisting load. The result is a more evenly distributed and accurate torque load compared to that of the head bolt. This ultimately translates into higher reliability and a lower chance of head gasket failure.

Engine Assembly

One of the main differences between head bolts and head studs involves the methods used to put together or repair an engine. Higher-end head studs that have been specially designed within exact tolerances are capable of securely positioning the head gasket and cylinders with near-perfect alignment. This feature makes it easier to assemble an engine using head studs. However, head bolts are far more convenient for disassembling an automobile engine or for performing maintenance, such as part replacement. Many everyday-use vehicles have master cylinders or other components that extend into the engine compartment. Under these specifications, head bolts allow the cylinders to be removed without removing the entire engine from the car, as is necessary with head studs.

In other words, head studs are better suited for high-performance vehicles with greater power requirements, while head bolts are more practical for personal, everyday automobiles. Therefore, it would be inaccurate to conclude that one type of fastener is categorically superior to the other. Rather, the preference depends on the automobile in question and the ways in which it will be put to use.

For racing enthusiasts, www.CircleTrack.com can provide more information on high-end engine fasteners.

How a Bolt Work

The bolt is a crucial component in modern manufacturing and has a vast range of applications in both commercial and industrial products, from airliners to gardening tools. Despite their seemingly straight forward role, bolts display a relatively complex combination of mechanical properties and design features that enable them to function properly.

A bolt’s utility is not determined simply by whether it fits into its hole or not, but rather a series of particular specifications. The type of bolt, its physical dimensions, thread density, forming material, and tightening requirements are all important characteristics for effective bolt installation. Likewise, the complementary linkage of nuts and bolts can be a significant influence on component assembly and product efficiency. Using a bolt that is too long might interfere with operations, while mounting one that lacks tensile strength may cause equipment to break down. Therefore, understanding how bolts accomplish their tasks can mean the difference between a successful project and an ineffective one. Bolt Threads

Threads are one of a bolt’s main characteristics. A thread functions under the basic concept of an inclined plane that is spiraled around the length of a fastener. This spiral requires rotational pressure to be inserted into a slot. Turning the bolt causes the threads to move the complementary slot or nut upward against the inclined plane. The greater the torque, or turning force, the greater the pressure pulling the nut forward along the threads. This in turn creates tension in the bolt and a clamping force that presses the two components together. A higher number or a denser arrangement of threads can strengthen the joint. In addition, cutting threads into the bolt after it has been heat-treated also improves thread strength. Mechanical Forces

The act of tightening a bolt engages several different types of mechanical force that help the resultant joint remain secure. The main forces generated by bolt installation include:

Clamping Force: This is a type of compression that the bolt applies to the joint, holding the two components together.

Preloading Force: Turning the bolt causes the threads to engage and stretch, which produces the preload force that keeps the threads in place.

Shear Force: The shear force is the transverse pressure working against the bolt in a perpendicular direction. It can be present alone or in combination with tension force.

Tension Force: Tension force applies to the length of the bolt, providing pressure along its vertical dimension, rather than its width.

The clamping force accomplishes the task of holding multiple parts together, and is determined by the difference between the preloading force and the tension force. When the strength of the tension force equals that of the preload force, the bolt fails and the joint breaks apart. Generally, higher preload force translates into higher clamping force, which makes for a stronger bolted joint. Ideally, precise bolt installation and tightening will create a joint that yields little or no direct shear force. More detailed equations can be found at Keeping It All Together. Manufactured for Strength

The American Society for Testing Materials (ASTM) sets most of the standards for bolt specifications in the U.S., including dimensions, forming materials, and post-fabrication finishing. Bolts are produced in a range of different lengths and can have a variety of head shapes, such as hex, oval, flat, or socket configurations. A bolt’s overall mechanical strength can be measured by the degree of strain at which it finally breaks, while its yield strength designates the level at which it bends or deforms. Although the overall, or tensile, strength is always higher than the yield strength, for a machine to run properly its bolts should have loads under the yield level. Bolts that have a wide disparity between their tensile and yield strength are considered flexible and will stretch to a relatively high degree before failing.

Bolts come in many varieties, such as T-Head or T-Slot bolts, and can be produced from a wide range of materials, but steel is the most common material used for most high-strength applications. Steel bolts are graded according to newtons per millimeter squared for tensile strength as compared to yield strength. For example, a steel bolt with a rating of 5.5 will provide roughly 500 newtons/mm2 of tensile strength and approximately 400 newtons/mm2 of yield strength. Other popular bolt materials, such as corrosion-resistant stainless steel, alloys, and composite materials can be rated in similar fashion.

The Evolution on Bolt Manufacturing

Like the screw, the bolt occupies an integral position in both industrial and everyday life. In fact, bolts and screws are used more than any other type of mechanical fastener, and they can be found in nearly every simple or complex machine. Although there is no absolute distinction, the difference between screws and bolts can be broadly defined as one of thread size and tapering. Bolts are generally larger and do not have tapered ends. In standard usage, a fastener that is torqued with a nut is usually considered a bolt.

Without bolts, we would not be able to hold together the frames of cars or the arms and backs of chairs. A device as common as a pair of scissors or as sophisticated as a particle accelerator would be rendered inoperable. The self-evident utility of the modern bolt makes it all the more interesting to discover how this object came to be so crucial to our way of life. In the United States alone, the bolt has undergone several distinct stages of development. The Origins of Bolt Production

Bolt usage can be traced back to ancient irrigation systems and construction projects, but metal bolts and screws did not become the standard until the early modern era. The first machines used to produce metal bolts resembled cutting lathes and were invented in France in the mid-sixteenth century. However, it wasn’t until the nineteenth century and the beginning of mass production that bolts became the norm in industrial manufacturing.

In the United States, the first systematic bolt manufacturing operation was founded by Micah Rugg in 1818. Rugg was a Connecticut blacksmith who developed a process of cutting and heating square iron bars into bolt-sized pieces. These workpieces were then smoothed along an anvil, and a die-cutting press was used to shape the bolt’s head and threads. Using machine tooling processes, such as drop hammering and die trimming, proved to be both time- and cost-efficient. By 1840, Rugg had sold several thousand bolts and expanded his operation to produce nearly 500 bolts a day.

Bolt Innovations

Following the success of Rugg’s pioneering bolt production methods, other manufacturers began developing new technologies and techniques to capitalize on the burgeoning fastener market. William Clark, another manufacturer from Connecticut, is credited with designing the first bolts and dies made from round, rather than square, iron in the 1860s. Clark also streamlined the bolt head formation process by using die compression to create both the head and the angled neck in the same operation. His pinched and concave neck bolts proved highly cost-efficient and reduced the risk of splitting wood when driving the bolts into a workpiece.

Some of the other new bolt configurations that emerged over the next thirty-year period included:

Star Bolt: This was a pinched neck bolt similar to Clark’s first design that eventually fell under his patent.

Bastard Neck Bolt: The bastard neck configuration had a thin bolt head and a short rectangular shank.

Fin-Head Bolt: This bolt was designed with narrow lugs underneath the head that helped keep it steady while a nut was being tightened or removed.

By 1905, there were over five hundred factories in the United States specializing in bolt and nut production. Part of the skyrocketing demand for bolts in the later half of the nineteenth century was driven by the spreading utility of new bolt designs.

Current Production Methods

The twentieth century saw the development of our present-day bolt manufacturing methods, particularly through the advances and armaments engendered by the two world wars. Although these techniques greatly expanded previous production capabilities, they were similar in principle to the original processes established in the 1800s. For example, the cold-forging technique used today hearkens back to the cold-forged fin-head bolts first developed in 1890.

The majority of current bolt manufacturing methods employ cold-forged heading to shape a steel workpiece. A gripping die holds the metal stock in place while a concave compression punch forms the bolt’s angled round head. The bolt’s shaft is then deformed through the thread rolling process, which uses cutting dies to shape threads into the metal shaft. The bolt is then usually coated with anti-corrosive substances to strengthen its durability. Hot or cold blackening and galvanization may be used to chemically bond a sealant, such as oil, onto the bolt in order to extend its working life. While these methods are more cost-efficient, boast higher production rates, and create less waste than the older methods of the nineteenth century, the modern-day bolt still owes its design and central attributes to the pioneering efforts of early manufacturers.

Gasket Material and Selection

Most major manufacturing sectors, including the automotive, aerospace, electronics, appliance, and military industries, employ gaskets in their production methods. A gasket is a sealing device made of deformable material usually designed in the form of a ring or sheet. Gaskets create a pressure-tight seam between multiple stationary components, relying on a compression seal to prevent unwanted gas or liquid emissions. These seals are often intended to be resistant to pressure, temperature fluctuations, and in some cases, electrical or electromagnetic forces. Since it uses compression, a gasket is typically more malleable than the components it joins and is able to conform to the shape of the harder surfaces between which it is placed.

Gaskets are available in a large number of specifications, making proper gasket selection an important step in many manufacturing processes. They can be formed from a wide range of materials, such as metals, rubbers, plastics, corks, foams, and composite substances. They also come in numerous designs, including jacketed, double-jacketed, spiral wound, and Kammprofile varieties. Finding the right combination of material and design depends on the gasket’s specific uses and the cost parameters of the project.

Is a Gasket Necessary?

While gaskets serve an important function as sealing joints, there are a handful of similar devices that may be better-suited to certain tasks. An application requiring a seal that forms a barrier between external and internal elements, such as a unit to prevent water leakage, usually needs a gasket. However, to fill small assembly gaps between components, manufacturers would be better served by a spacer, or “shim,” which is a narrow wedge used for packing or leveling purposes.

Likewise, o-rings, though similar to gaskets, have a subtly different designation. Unlike gaskets, o-rings are made almost exclusively of synthetic rubber or plastic polymers with elastomeric properties, and are produced solely in ring form. They are durable and reliable in sealing matched components by creating a barrier around an area with leakage potential. In addition, o-rings are distinct for their round or square cross-sectional configurations, as well as their high pressure resistance, making them valuable in some applications where a standard gasket’s resistance would not suffice.

Gasket Specifications

After determining that a gasket—as opposed to a shim or an o-ring—is the appropriate device for a given application, several other factors must be taken into account to choose a well-suited design. There are numerous types of gaskets, though many share similar features and may be capable of handling related tasks. Some of the most common varieties of gasket include:

Jacketed Gaskets: This form merges the efficiency and flexibility of soft gaskets (made of rubber or plastic) with the resistance and durability of an external metal coating. A single-jacket has soft filler with metal coverage along one face of the gasket, while a double-jacketed version has a fully coated metal facing, providing improved temperature, pressure, and corrosion resistance. Other variations include corrugated jacketed gaskets, and French Style jackets, which provide coating on either the inside or outside of the gasket.

Solid Gaskets: Solid gaskets are typically formed of metal and are a relatively inexpensive alternative to jacketed gaskets. They have high thermal and pressure resistance, though they require higher compression force to form a seal and are usually effective only against surfaces that are harder than the metal itself.

Spiral Wound Gaskets: This type of gasket is formed by combining metal with softer plastics or synthetic rubber in a winding shape, often reinforced with additional layers of metal without filler. Its unique design yields high thermal and physical stress resistance, coupled with flexibility and resilient sealing. Spiral wound gaskets are often used in piping, pumping, and heat exchange systems.

Kammprofile Gaskets: The Kammprofile design contains a corrugated metal core covered with a malleable sealing material attached to both of its sides. This structure focuses physical stress onto the surface sealant, creating tight seals along the gasket’s edges while retaining the device’s flexibility and strong tensile core. Kammprofile gaskets provide reliable support in heat exchange systems and have improved cost-effectiveness due to their capacity for repair.

Metal Gaskets

Many types of gaskets are constructed from metal or a mixture of metal and non-metal materials. These gaskets are typically formed with aluminum, copper, nickel, steel, stainless steel, or brass. These materials provide a high level of thermal, corrosive, and pressure resistance, along with excellent durability and tensile strength. On the other hand, metals require elevated amounts of compressive force to form a seal and have limited flexibility for multiple applications. For these reasons, metals are often used in combination with rubber or plastic compounds, otherwise known as “soft fillers.” Rubber and Plastic Gaskets

Due to its elastomeric properties, rubber is a popular material for gasket production. Since they can undergo a high degree of deformation without permanent damage or loss of attributes, rubber gaskets can form very tight seals within a wide range of applications. Some types of rubber frequently used in gasket manufacturing include nitril, viton, and neoprene. Certain polymers, such as thermoplastic elastomer, thermoplastic rubber, and polyvinyl chloride, display qualities similar to those of rubber and are also common in gasket production. Silicone Gaskets

Silicone is a valuable gasket material because it displays strong resistance to extreme temperatures. Silicone-based gaskets can have operating temperatures that range between roughly -140 degrees to 480 degrees Fahrenheit. In addition, their resistance to ultraviolet light makes them useful in outdoor settings, while their flame tolerance within a certain thickness range has applications in electronics and transit industries. Silicone gaskets come in foam and sponge varieties, and can be reinforced with other materials to improve tensile strength or adjust thermal and electrical conductivity. Compression Testing

An important characteristic for industrial gaskets is their capacity for tolerating compressive loads. Evaluations, such as the hot compression test, can be used to gauge a specific gasket’s ability to withstand various weights and temperatures. Typically, a gasket is placed between the exertion bolts of a hydraulic press. Temperature is increased, often up to nearly 600 degrees Fahrenheit, at an incremental rate over a given period of time while the press exerts constant load pressure on the gasket. Any decreases in material thickness are measured and used to assess the gasket’s effectiveness. Tests such as this can be helpful in selecting a gasket or deciding upon a given material or design configuration.

Torque Tensioning

Torque Tensioning

When bolts are fastened to a device or structure, they require a certain amount of preload torque tension in order to properly support the final load. Preload tension is the amount of tension applied to the bolt by a device like a torque wrench or spanner that tightens the bolt into place before the load it will eventually support is added (thus, preload). It is important to apply the correct amount of preload tension when fastening a bolt in order to meet the requirements of the specific bolt material and grade, the load it will carry, and many other aspects of the load. If proper preload conditions aren’t met, a bolt may fail or a unit may become damaged because of the inadequate fastening.

In order to properly fasten bolts, it is important to follow standards for torque tension. The SAE International has outlined a series of standards both for bolt sizes and torque tension on these bolts in relation to the substrate material.

SAE Bolt Standards (a sample)

These grades are available at http://www.unified-eng.com/scitech/bolt/boltmarks.html. The SAE

Fastener Standards Manual can be purchased directly from SAE at this website:

http://books.sae.org/book-hs-4000/2009. It features more gradings for bolts as well as other fasteners.

In order to make torque tensioning standards effective, a little physics is involved. Two different equations are used to determine the force needed.

For a reusable connection: Fi = 0.75AtSp

For a permanent connection: Fi = 0.9AtSp In these equations, Fi is the “recommended preload force.” At is the tensile area of the bolt and Sp is the proof strength of the bolt. This equation can be difficult to solve due to the difficulty measuring Fi, but there is another equation that can help figure it out.

T = K Fi d In this equation, d is the nominal diameter of the bolt and K is a known variable, the correction factor that depends on the material, size, surface friction and threading of the bolt. Most bolts have a 0.15 to 0.3 K. The following chart shows various K values for different materials:

material

K value

unlubricated mid-size steel bolt

• 0.20

non-plated black finish

0.30

zinc-plated

0.20

cadmium-plated

0.16

lubricated

0.15-0.18

Based on this information, we can determine different torque tension needs for different grades of bolts. For instance, a grade 8 bolt used on three different materials:

Example SAE Torque Tensioning Standards

Grade

Material and K value

Nominal size and Threads per inch

Stress Area in squared inches

Torque in inches per pound

8

k=0.2

0.138-40

0.01014

23.4

8

k-0.15

.138-40

0.01014

17.6

More sample information is available at http://www.gizmology.net/nutsbolts.htm. For more SAE bolt torque tensioning standards, consult the manual on sale at the SAE International website at http://books.sae.org/book-hs-4000/2009.

The History Of Zipper

Manufacturers produce zippers by the billions each year, but the device wasn’t always such a success. In the early stages of development, zippers went through design revisions, unsuccessful marketing attempts and a few name changes. Zippers are abundant today due to the tremendous patience of investors, an engineer who gave the product its crucial final touches and World War I, when the zipper was mass produced for the first time.

First Zipper Versions

The first semblance of a zipper model traces back to Elias Howe, the founder of the sewing machine. In 1851, he created a patent for a device named An Automatic Continuous Clothing Closure, which had a similar function to the modern zipper, although the composition was significantly different. The product operated as individual clasps that were joined manually, and pulled shut by using a string, creating a “gathered” effect. Ultimately, Howe did not continue developing his model, and several years went by before another patent was created.

More than 40 years later, inventor Whitcomb L. Judson began devising the patent “Clasp Locker or Unlocker for Shoes.” The design was essentially a guide (now known as a fastener or slider) that was used to close the space between a shoe’s clasps on one side to the attachments on the other. The guide could be removed after use, and had the double function of pushing the bulky clasps down and subsequently pulling them together to close. The guide was difficult to produce due to its very specific functions, and was also seen as time consuming.

Whitcomb’s second patent in 1893 was a transition from the former bulky clasps to hooks and eyes. This device, later called “C-curity” was a series of loops (short metal extensions) that were manually laced into the boot or shoe. The improvement was significant because the device functioned as a unit instead of as individual clasps. Eventually, it proved to be ineffective because it had a tendency to spring open.

Engineer Gideon Sundback ultimately enhanced the previous zipper models by devising a model called the “Plako fastener.” The design featured oval hook units that would protrude from the tape they were attached to, and provided a more secure fit than the previous “C-curity” design. Although the model had a tighter fit, it was not flexible. Also, it did not stay closed when it was bent and posed some of the same problems as the earlier hook design.

The Final Design and Production

In 1913, Sundback revised and introduced a new model, which had interlocking oval scoops (instead of the previously used hooks) that could be joined together tightly by a slider in one movement or swoop. This final model is recognized as the modern zipper, which took many months to find success in the industrial market. Retailers, who were prone to sticking with traditional materials and design methods, were slow to purchase the product. In the early stages of production, zippers were used exclusively for boots and tobacco pouches. During World War I, military and navy designers acquired zippers for flying suits and money belts, ultimately helping the reputation of the device’s durability. It was B.F. Goodrich, (which used the product for boots and galoshes in the 1920’s) that gave the device the name zipper, after the sound, or “zip” that the slider created.

Originally, manufacturers produced metal zippers, which are effective when used for heavy weight or thick materials. These metal zippers were made in aluminum, nickel and brass and were eventually incorporated into every day wear, such as denim. Designers accelerated the success of zippers with even more materials, such as plastic zippers, which are soft, pliable and easy to maintain. Gradually, manufacturers saw the product’s selling ability and versatility, and zippers, now available in a variety of materials and designs like coils and colored metallic, finally achieved widespread success.