Screwdriver

From Wikipedia, the free encyclopedia
Jump to: navigation, search
For other uses, see Screwdriver (disambiguation).
Screwdriver
Screw Driver display.jpg
A slotted or "flat-blade" screwdriver
Other names Turnscrew
Classification Hand tool
Types See shape chart below
Related Hex key
Wrench

A screwdriver is a tool, manual or powered, for turning (driving or removing) screws. A typical simple screwdriver has a handle and a shaft, and a tip that the user inserts into the screw head to turn it. 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'. Handle are typically wood, metal, or plastic[1] 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—slots, grooves, recesses, etc.—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 (List of screw drives). The two most common are the simple 'blade'-type for slotted screws, and Phillips.

A wide variety of power screwdrivers range from a simple 'stick'-type with batteries, a motor, and a tip holder all inline, to powerful "pistol" type VSR (variable-speed reversible) 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[edit]

The earliest documented screwdrivers were used in Europe 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 (screwturner) and tournevis (turnscrew), respectively. The first documentation of the tool is in the medieval Housebook of Wolfegg Castle, a manuscript written sometime between 1475 and 1490.[2] These earliest screwdrivers had pear-shaped handles and were made for slotted screws (diversification of the many types of screwdrivers did not emerge until the Gilded Age). 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.[further explanation needed]

The jaws that hold the pyrites inside medieval guns were secured with screws, and the need to constantly replace the pyrites resulted in 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.

Illustration from Robertson's patent application

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 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 carved 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.

Close-up of Robertson screw

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 a favorite of mechanics today 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.

Phillips screw head

Meanwhile, 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 onslaught 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 refer to a screwdriver as a turnscrew, under which name it is an important part of a set of pistols. The name was common in earlier centuries, used by cabinet makers, shipwrights, and perhaps other trades. The cabinet-maker'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.

Drive types[edit]

A jeweler's screwdriver
A set of "secure" or otherwise less common screwdriver bits, including secure Torx and secure hex or "allen" variants.
Main article: List of screw drives

Screwdrivers come in a large range of sizes to accommodate various screws—from tiny jeweler'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. This is less important for PoziDriv and SupaDriv, which are designed specifically to tolerate some size mismatch.

Some screwdriver tips are magnetic, so that the screw remains attached to the screwdriver without requiring external force. This is particularly useful in small screws, which are otherwise difficult to handle. Many screwdriver designs have a handle with detachable tip (the part of the screwdriver that engages the screw), called bits as with drill bits. This provides a set of one handle and several bits that can drive a variety of screw sizes and types.

Many modern electrical appliances, if they contain screws, use screws with heads other than the typical slotted or Phillips styles. Torx is one such pattern that has become widespread. The main cause of this trend is manufacturing efficiency: Torx screws do not slip out of the fastener as easily as a Phillips or slotted driver (Slotted screws are rarely used in mass-produced devices, since the driver is not inherently centered on the fastener.) Non-typical fasteners are commonplace in consumer devices for their ability to make disassembly more difficult, which is seen as a benefit for manufacturers but is considered a disadvantage by users than if more-common head types were used. However, Torx and other drivers have become widely available to the consumer due to their increasing use in the industry. Specialized patterns of security screws are also used, such as the Line Head (LH) style by OSG System Products, Japan, as used in many Nintendo consoles, though drivers for the more common security heads are, again, readily available.

Handle[edit]

"Perfect Handle" screwdrivers

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"[further explanation needed] screwdriver was first manufactured by HD Smith & Company, which operated from 1850 to 1900. Many manufacturers adopted this handle design. The "flat bladed" screwdriver was another design 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 an in-line nut 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. The offset screwdriver has a handle set at right angles to the small blade, providing access to narrow spaces and giving extra torque.

A screwdriver can be used in either hand. There is no such thing as a "left-handed screwdriver"; being sent to find one is a fool's errand, often used as a test of stupidity, or as a metaphor for something useless. In the UK, the term "Birmingham screwdriver" (like "Glasgow socket set") jokingly denotes a hammer or sledgehammer.[3]

Blade types[edit]

Main article: List of screw drives

The tool used to drive a slotted screw head is called a common blade, flat-blade, slot-head, straight, flat, flat-tip,[4] or "flat-head"[5] 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. Such a flat-headed screw may have a slotted, cross, square recessed, or combination head. Prior to the development of the newer bit types the flat-blade was referred to as the "Common-Blade". This was simply because it was the most common one.

Among slotted screw drivers, variations at the blade or bit end involve the profile of the blade as viewed face-on (from the side of the tool). The more common type is sometimes referred to as 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. 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 fit a particular screw for a tighter engagement and reduce screw head deformation. However, many better-quality screwdriver blades are already induction-hardened (surface heat-treated), and tip grinding after manufacture compromises their durability. Thus, it is best to select a tip made to fit precisely to begin with, and avoid weakening the factory heat-treatment.

Frearson vs Phillips.svg

Phillips screwdrivers come in several standard sizes, ranging from tiny "jeweler's" to those used for automobile frame assembly—or #00 to #3 respectively. This size number is usually stamped onto the shank (shaft) or handle for identification. Each bit size fits a range of screw sizes, more or less well. Each Phillips screwdriver size also has a related shank diameter. The driver has a 57° point and tapered, unsharp (rounded) flutes. By far the most commonly found size around the household, automobile, and office is the #2, —which fits computers, printers and photocopiers, light switches, carburetors, furniture, household appliances, door hinges, and so forth. The second most commonly seen household Phillips screw is the #1, which fits calculators, cameras, smaller toys, and cell phone sized devices. The #1 and smaller bits come to a blunt point, but the #2 and above have no point, but rather a nearly squared-off tip, making each size incompatible with the other. A "#2 x 6 Phillips screwdriver" designation as commonly seen in tool catalogs describes a Number Two bit with a six-inch-long shank.

The rounded, tapered slots of the Phillips head were deliberately designed for the screwdriver to "cam out" (pop out) of the screw head recess under high torque on high-speed factory assembly lines.[6] This prevents stripping damage to the screw threads, at the expense of possible damage to the recess in the screw head. Modern torque-limiting power driver tools for professional use eliminate overtorquing damage much more reliably. Market inertia and ignorance of the design's historical intent have led to widespread misapplication of Phillips head fasteners in applications where cam-out is not desirable. Some Phillips head screwdrivers have been manufactured with hardened "anti-cam-out" (ACO) grooves in an attempt to defeat this designed-in behavior.[7] See torx head screw.

Robertson, also known as a square,[8] or Scrulox[9] screw drive has a square-shaped socket in the screw head and a square protrusion on the tool. Both the tool and the socket have a taper, which makes inserting the tool easier, and also tends to help keep the screw on the tool tip without the user needing to hold it there. (The taper's earliest reason for being was to make the manufacture of the screws practical using cold forming of the heads,[10] but its other advantages helped popularize the drive.) Robertson screws are commonplace in Canada, though they have been used elsewhere [11] and have become much more common in other countries in recent decades. Robertson screwdrivers are easy to use one-handed, because the tapered socket tends to retain the screw, even if it is shaken.[11] They also allow for the use of angled screw drivers and trim head screws. The socket-headed Robertson screws are self-centering, reduce cam out, stop a power tool when set, and can be removed if painted-over or old and rusty.[11] In industry, they speed up production and reduce product damage. One of their first major industrial uses was the Ford Motor Company's Model A & Model T production. Henry Ford found them highly reliable and saved considerable production time, but when he couldn't secure licensing for them in the United States, limited their production use to his Canadian division. Robertson-head screwdrivers are available in a standard range of tip-sizes, from 1.77mm to 4.85mm.

Reed and Prince, also called Frearson, is another historic cross-head screw configuration. The cross in the screw head is sharper and less rounded than a Phillips, and the bit has 45° flukes and a sharper, pointed end. Also, the Phillips screw slot is not as deep as the Reed and Prince slot.[12][13][14] In theory, different size R&P screws fit any R&P bit size.[15]

Pozidriv and the related Supadriv are widely used in Europe and most of the Far East.[16] While Pozidriv screws have cross heads like Phillips and are sometimes thought effectively the same, the Pozidriv design allows higher torque application than Phillips. It is often claimed that they can apply more torque than any of the other commonly used cross-head screwdriver systems, due to a complex fluting (mating) configuration.

Japanese Industrial Standard (JIS) cross-head screwdrivers are still another standard, often inaccurately referred to as Japanese Phillips. Compatible screw heads are usually identifiable by a single depressed dot or an "X" to one side of the cross slot. This is a screw standard throughout the Asia market and Japanese imports. The driver has a 57° point with a flat tip.[17]

Variations[edit]

Torque screwdrivers[edit]

Main article: Torque screwdriver

Screwdrivers are available—manual, electric, and pneumatic—with a clutch that slips at a preset torque. This helps the user tighten screws to a specified torque without damage or over-tightening. Cordless drills designed to use as screwdrivers often have such a clutch.

Powered screwdrivers[edit]

A rechargeable battery-powered electric screwdriver.
An auto-feed, battery-powered screwdriver

Interchangeable bits allow the use of powered screwdrivers, commonly using an electric or air motor to rotate the bit. Cordless drills with speed and torque control are commonly used as power screwdrivers.

Ratcheting screwdrivers[edit]

Some manual screwdrivers have a ratchet action whereby the screwdriver blade locks to the handle for clockwise rotation, but uncouples for counterclockwise rotation when set for tightening screws—and vice versa for loosening.

Stanley Yankee No 130A, spiral or ratchet screwdriver

Spiral ratchet screw drivers, often colloquially called Yankee Screwdrivers (a brand name), provide a special mechanism that transforms linear motion into rotational motion. Originally the "Yankee" name was used on all tools sold by the North Brothers Manufacturing Company but later, after Stanley purchased the company, it became synonymous with only this type of screwdriver. The user pushes the handle toward the workpiece, causing a pawl in a spiral groove to rotate the shank and the removable bit. The ratchet can be set to rotate left or right with each push, or can be locked so that the tool can be used like a conventional screwdriver. One disadvantage of this design is that if the bit slips out of the screw, the resultant sudden extension of the spring may cause the bit to scratch or otherwise damage the workpiece.

Once very popular, versions of these spiral ratchet drivers using proprietary bits have been largely discontinued by manufacturers such as Stanley. Some companies now offer a modernized version that uses standard 1/4-inch hex shank power tool bits. Since a wide variety of drill bits are available in this format, the tool can do double duty as a "push drill" or Persian drill.

Misuse[edit]

Manual straight screwdrivers are commonly abused as improvised substitutes for other tools, such as crow bars or chisels. Screwdrivers are not designed for these purposes, and such use can damage the tip, bend the shaft, or injure the user if the screwdriver slips or breaks.[18]

Screwdrivers have been used as stabbing weapons,[19][20] and are usually tightly restricted in prisons.

See also[edit]

References[edit]

  1. ^ http://www.britannica.com/EBchecked/topic/529926/screwdriver
  2. ^ Rybczynski 2000, pp. 90–94.
  3. ^ Green, Jonathon (1998). Dictionary of Slang. Cassell. 
  4. ^ Capotosto, Rosario (December 1996), "Screwdriver Basics", Popular Mechanics 173 (12): 82–83, ISSN 0032-4558. 
  5. ^ Review, Princeton (2004). Cracking the ASVAB. New York: Random House. p. 174. ISBN 978-0-375-76430-1. 
  6. ^ Alfred, Randy (2011-07-07). "July 7, 1936: Get a Grip — Phillips Screws Up the Toolbox". Wired:This Day in Tech (Conde Nast Digital). Retrieved 2012-03-11. Henry F. Phillips receives patents for a new kind of screw and the new screwdriver needed to make it work. 
  7. ^ "Anti Cam Out Screwdriver Tips – "ACO" & "ACR"". ToolGuyd. ToolGuyd.com. Retrieved 2012-03-11. 
  8. ^ Furniture Projects for the Deck and Lawn. Cambium Press. 2004. ISBN 9-78189-283-617-5. Retrieved 2012-03-12. 
  9. ^ Robertson Inc. "Robertson Inc. - The Original Robertson Fastening System". Robertson Inc. main site. Retrieved 2011-09-28. 
  10. ^ Rybczynski 2000, pp. 79–81.
  11. ^ a b c Rybczynski 2000, pp. 85–86
  12. ^ "The Phillips screwdriver has about 30° flukes and a blunt end, while the Reed and Prince has 45° flukes and a sharper, pointed end." RECESSED www.tpub.com October 2011
  13. ^ Michael Uva (2010). The Grip Book. Taylor & Francis. ISBN 9 78024 081 291 5. Retrieved 2014-09-14. 
  14. ^ "Reed and Prince Screwdriver". www.scribd.com. 
  15. ^ "Bits From MRO Tools". mrotools.com. The Frearson recess is designed so that any size bit will fit any size recess. 
  16. ^ "When a Phillips is not a Phillips, step13: Posidriv". instructibles.com. 
  17. ^ "When a Phillips is not a Phillips, step10: JIS – Japanese Industrial Standard". instructibles.com. October 2011. 
  18. ^ Klein Tools. "Proper Use and Care of Hand Tools: Screwdrivers". Retrieved 2010-03-15. 
  19. ^ "Offensive Weapons-Knives and Offensive Weapons". Crown Prosecution Service (UK). January 2012. Retrieved 13 September 2014. —includes cases of attacks with screwdrivers used as offensive weapons, See section: "R. v Parkin [2010] EWCA Crim 2280"
  20. ^ Hendrick, Thomas (February 7, 2014). "Man sentenced to life in prison for screwdriver stabbing". KDVR.com (FOX 31-Denver). Retrieved September 14, 2014. 

Bibliography[edit]