Screwdriver
A screwdriver is a tool, manual or powered, used for turning screws.
Description
A typical simple screwdriver has a handle and a shaft, ending in a tip the user puts into the screw head before turning the handle. This form of the screwdriver has been replaced in many workplaces and homes with a more modern and versatile tool, a power drill, as they are quicker, easier, and can also drill holes. The shaft is usually made of tough steel to resist bending or twisting. The tip may be hardened to resist wear, treated with a dark tip coating for improved visual contrast between tip and screw—or ridged or treated for additional "grip".Handles are typically wood, metal, or plastic and usually hexagonal, square, or oval in cross-section to improve grip and prevent the tool from rolling when set down. Some manual screwdrivers have interchangeable tips that fit into a socket on the end of the shaft and are held in mechanically or magnetically. These often have a hollow handle that contains various types and sizes of tips, and a reversible ratchet action that allows multiple full turns without repositioning the tip or the user's hand.
A screwdriver is classified by its tip, which is shaped to fit the driving surfaces on the corresponding screw head. Proper use requires that the screwdriver's tip engage the head of a screw of the same size and type designation as the screwdriver tip. Screwdriver tips are available in a wide variety of types and sizes. The two most common are the simple 'blade'-type for slotted screws, and Phillips, generically called "cross-recess", "cross-head", or "cross-point".
A wide variety of power screwdrivers ranges from a simple "stick"-type with batteries, a motor, and a tip holder all inline, to powerful "pistol" type VSR cordless drills that also function as screwdrivers. This is particularly useful as drilling a pilot hole before driving a screw is a common operation. Special combination drill-driver bits and adapters let an operator rapidly alternate between the two. Variations include impact drivers, which provide two types of 'hammering' force for improved performance in certain situations, and "right-angle" drivers for use in tight spaces. Many options and enhancements, such as built-in bubble levels, high/low gear selection, magnetic screw holders, adjustable-torque clutches, keyless chucks, "gyroscopic" control, etc., are available.
History
The earliest documented screwdrivers were used in the late Middle Ages. They were probably invented in the late 15th century, either in Germany or France. The tool's original names in German and French were Schraubendreher and tournevis, respectively. The first documentation of the tool is in the medieval Housebook of Wolfegg Castle, a manuscript written sometime between 1475 and 1490. These earliest screwdrivers had pear-shaped handles and were made for slotted screws. The screwdriver remained inconspicuous, however, as evidence of its existence throughout the next 300 years is based primarily on the presence of screws.Screws were used in the 15th century to construct screw-cutting lathes, for securing breastplates, backplates, and helmets on medieval jousting armor—and eventually for multiple parts of the emerging firearms, particularly the matchlock. Screws, hence screwdrivers, were not used in full combat armor, most likely to give the wearer freedom of movement.
The jaws that hold the pyrites inside wheellock guns were secured with screws, and the need to constantly replace the pyrites resulted in a considerable refinement of the screwdriver. The tool is more documented in France, and took on many shapes and sizes, though all for slotted screws. There were large, heavy-duty screwdrivers for building and repairing large machines, and smaller screwdrivers for refined cabinet work.
The screwdriver depended entirely on the screw, and it took several advances to make the screw easy enough to produce to become popular and widespread. The most popular door hinge at the time was the butt-hinge, but it was considered a luxury. The butt-hinge was handmade, and its constant motion required the security of a screw.
Screws were very hard to produce before the First Industrial Revolution, requiring the manufacture of a conical helix. The brothers Job and William Wyatt found a way to produce a screw on a novel machine that first cut the slotted head, and then cut the helix. Though their business ultimately failed, their contribution to low-cost manufacturing of the screw ultimately led to a vast increase in the screw and the screwdriver's popularity. The increase in popularity gradually led to refinement and eventually diversification of the screwdriver. Refinement of the precision of screws also significantly contributed to the boom in production, mostly by increasing its efficiency and standardizing sizes, important precursors to industrial manufacture.
Canadian P.L. Robertson, though he was not the first person to patent the idea of socket-head screws, was the first to successfully commercialize them, starting in 1908. Socket screws rapidly grew in popularity, and are still used for their resistance to wear and tear, compatibility with hex keys, and ability to stop a power tool when set. Though immensely popular, Robertson had trouble marketing his invention to the newly booming auto industry, for he was unwilling to relinquish his patents.
Meanwhile, in Portland, Oregon, Henry F. Phillips patented his own invention, an improved version of a deep socket with a cruciform slot, today known as the Phillips Screw. Phillips offered his screw to the American Screw Company, and after a successful trial on the 1936 Cadillac, it quickly swept through the American auto industry. With the Industrial Revival at the end of the Great Depression and the upheaval of World War II, the Phillips screw quickly became, and remains, the most popular screw in the world. A main attraction for the screw was that conventional slotted screwdrivers could also be used on them, which was not possible with the Robertson Screw.
Gunsmiths still call a screwdriver a turnscrew, under which name it is an important part of a set of pistols. The name was common in earlier centuries, used by cabinetmakers, shipwrights, and perhaps other trades. The cabinetmaker's screwdriver is one of the longest-established handle forms, somewhat oval or ellipsoid in cross-section. This is variously attributed to improving grip or preventing the tool rolling off the bench. The shape has been popular for a couple of hundred years. It is usually associated with a plain head for slotted screws, but has been used with many head forms. Modern plastic screwdrivers use a handle with a roughly hexagonal cross-section to achieve these same two goals, a far cry from the pear-shaped handle of the original 15th-century screwdriver.
Handle
The handle and shaft of screwdrivers have changed considerably over time. The design is influenced by both purpose and manufacturing requirements. The "Perfect Pattern Handle" screwdriver was first manufactured by HD Smith & Company, which operated from 1850 to 1900. Many manufacturers adopted this handle design. At the time, the "flat bladed" screw type was prevalent and was the fastener with which they were designed to be used. Another popular design was composed of drop-forged steel with riveted wood handles.The shape and material of many modern screwdriver handles are designed to fit comfortably in the user's hand, for user comfort and to facilitate maximum control and torque. Designs include indentations for the user's fingers, and surfaces of a soft material such as thermoplastic elastomer to increase comfort and grip. Composite handles of rigid plastic and rubber are also common. Many screwdriver handles are not smooth and often not round, but have flats or other irregularities to improve grip and to prevent the tool from rolling when on a flat surface.
Some screwdrivers have a short hexagonal section at the top of the blade, adjacent to the handle, so that a ring spanner or open wrench can be used to increase the applied torque. Another option are "cabinet" screwdrivers which are made of flat bar stock and while the shaft may be rounded, will have a large flat section adjacent to the handle which a wrench may be used on for additional leverage. The offset screwdriver has a handle set at right angles to the small blade, providing access to narrow spaces and giving extra torque.
Drive tip
Screwdrivers come in a large range of sizes to accommodate various screws—from tiny jeweller's screwdrivers up. A screwdriver that is not the right size and type for the screw may damage the screw in the process of tightening it.Some screwdriver tips are magnetized, enabling them to retain ferromagnetic screws. This aids both insertion and removal, and is particularly useful when handling small screws or working in confined spaces. Many screwdriver designs employ interchangeable tips, known as screwdriver bits, analogous to drill bits. This allows a single handle to be used with multiple bits of varying profiles and dimensions, enhancing the tool’s versatility.
Slotted
The tool used to drive a slotted screw head is called a standard, common blade, flat-blade, slot-head, straight, flat, flat-tip, or "flat-head" screwdriver. This last usage can be confusing, because the term flat-head also describes a screw with a flat top, designed to install in a countersunk hole. Before the development of the newer bit types, the flat-blade was called the "Common-Blade", because it was the most common one. Depending on the application, the name of this screwdriver may differ. Within the automotive/heavy electric industries, it is known as a "flat head screwdriver"; within the avionics and mining industries, it is known as a "standard screwdriver". Though there are many names; the original device from 1908 was known as a "flat-head screw turner".Among slotted screwdrivers, variations at the blade or bit end involve the profile of the blade as viewed face-on. The more common type is sometimes called keystone, where the blade profile is slightly flared before tapering off at the end, which provides extra stiffness to the workface and makes it capable of withstanding more torque by gripping deeper in the screw slot. To maximize access in space-restricted applications, the cabinet variant screwdriver blade sides are straight and parallel, reaching the end of the blade at a right angle. This design is also frequently used in jeweler's screwdrivers.
Many textbooks and vocational schools instruct mechanics to grind down the tip of the blade, which, due to the taper, increases its thickness and consequently allows more precise engagement with the slot in the screw. This approach creates a set of graduated slotted screwdrivers that will fit a particular screw for a tighter engagement and reduce screw head deformation. However, many better-quality screwdriver blades are already induction-hardened, coated with black-oxide, black-phosphate, or diamond-coated to increase friction between the screwdriver tip and the screw. Thus tip grinding after manufacture will likely compromise their durability so it is best to select the proper tip and avoid weakening the manufacture's treatments.