Screwdriver



Background

It would be very difficult to find an American household that did not have at least one screwdriver. Perhaps the most ubiquitous of hand tools, the screwdriver has a long genealogy, the result of a complicated manufacturing process. Archimedes is considered to have invented the screw in the third century B.C. , though his invention was designed to transfer motion (as in the continuous worm of a worm and gear assembly) rather than to fasten things together.

By the first century B.C. , large wooden screws were used in presses for producing wine and olive oil, and were turned with spikes stuck into or through a handle that resembled a modern corkscrew used for opening wine bottles, although larger. These were made of wood with a flat rather than a pointed end, and a container to hold the material being pressed.

Metal screws and nuts seem to have been used as fasteners in the fifteenth century, although the heads of these screws were turned with a wrench and not a screwdriver—the screw heads were either square or hexagonal. Screws with slots in their heads were found in armor in the following century, although the design of the tool used to work the screws, the screwdriver, is unknown.

The modern screwdriver descends directly from a flat-bladed bit used in a carpenter's brace circa 1750. Woodworkers were using hand screwdrivers in the early 1800s, and they became more common after 1850, when machines made the automatic production of screws possible. These early screwdrivers were flat throughout the length of their shaft; the current design of a rounded bar that is flattened or shaped only at the working end makes the tool much stronger and takes advantage of the round wire used in its manufacture. The oldest and most common type of screwdriver is the slotted screwdriver, which fits a screw with a single slot in the head. There are perhaps thirty different types of screwdrivers available today in a variety of sizes, all with different purposes and all designed to fit into special screws.

The second most widely used screwdriver, the "Phillips," was invented in the late 1920s by Henry Phillips. Soon after its introduction, the tool posed a dilemma for its user—the head of the driver pulls away from the screw as it is fastened, or "cam-out," leading to stripped screw heads and assemblies that are difficult to take apart. However, cam-out became a virtue; the screws were meant to be driven with a power tool, and the assembler would know that the screw was completely driven when his power tool slid out of the screw head. A screw head that could accept the greater torque (turning power) of a power tool was an advantage over hand-turned, slotted screw heads. Today, manufacturers are producing or gearing up production of Phillips screwdrivers that eliminate cam-out. Possible solutions (although details of some systems are company secrets) focus on the angle of the edges that fit into the Phillips screw, or using a better gripping material to coat or plate the screwdriver tip.

The torx screwdriver, widely used for automobile repair and other applications, was designed to take the torque that a Phillips screw can while eliminating the cam-out problem. It has six edges in a star pattern on its flat point, and fits flat into the screw head.

To make the steel rod, wire is machine-drawn to the appropriate diameter, annealed (heat-treated), straightened, and then cold-formed to the proper shape. The cold forming press cuts the wire to the desired length and forms the tip of the screwdriver and the "wings" that will fit into the handle. The rod is then nickel-plated to give it a protective finish.
To make the steel rod, wire is machine-drawn to the appropriate diameter, annealed (heat-treated), straightened, and then cold-formed to the proper shape. The cold forming press cuts the wire to the desired length and forms the tip of the screwdriver and the "wings" that will fit into the handle. The rod is then nickel-plated to give it a protective finish.
It is not unusual to find torx drivers sold in a set with slotted and Phillips screwdrivers.

Other types of screwdrivers have been designed for special uses, and a well-stocked hardware store will have slotted, Phillips, torx, Robertson (a square shaft that fits into a corresponding square cut out in the head of the screw), and other more obscure types of screwdrivers. Some screwdrivers have not found a ready market, such as one that was designed to fit into special screws that have slots both on the top of the screw and on the side of the screw head, with corresponding grippers on the point of the screwdriver. There are so many screwdrivers and types of screws available that even a high quality of design innovation is overcome by consumer resistance to purchasing new types of screwdrivers and corresponding screws.

Raw Materials

The raw materials for most screwdrivers are very basic: steel wire for the bar and plastic (usually cellulose acetate) for the handle. In addition, the steel tips are generally plated with nickel or chromium.

The Manufacturing
Process

Making a flat-tip or slotted screwdriver is not very different than making any other configuration. Variations between a flat-tip and a Phillips screwdriver will be discussed later in this entry.

Making the steel bar

The plastic handles are made by mixing cellulose acetate with a plasticizer and then extruding the mixture into bar form. After further shaping, the bars are drilled so that the rods can be inserted, cleaned to remove dirt, and dipped in an acetone vapor bath, which melts and smooths the outside of the handle.
The plastic handles are made by mixing cellulose acetate with a plasticizer and then extruding the mixture into bar form. After further shaping, the bars are drilled so that the rods can be inserted, cleaned to remove dirt, and dipped in an acetone vapor bath, which melts and smooths the outside of the handle.

Phillips screwdrivers

Handles

Assembly

Quality Control

Consumer Reports magazine found, in 1983 tests, that the type of finish had little effect on the quality of screwdrivers, although most of their tested screwdrivers were plated. Poor-quality plating, on the other hand, might indicate that not enough care was paid to the tool in the manufacturing process. Similarly, poor-quality grinding can lead to rounded edges and corners which will not be as efficient as they could be; a tip that was burned during the grinding process may not be as hard as it should be.

Where To Learn More

Books

Hoffman, E. Fundamentals of Tool Design. T/C Publications, 1984.

Pollack, Herman W. Tool Design. Prentice Hall, 1988.

Self, Charles R. Fasten It. TAB Books, 1984.

Watson, Aldren A. Hand Tools: Their Ways and Workings. Portland House, 1982.

Periodicals

Bailey, Jeff. "Does Henry Phillips, Bane of Handymen, Really Rest in Peace?" Wall Street Journal, September 15, 1988, p. 4.

"Screwdrivers," Consumer Reports. January, 1983, pp. 44-7.

Kinghorn, Bob. "The New Age of Screwdriving," Family Handyman. October, 1989, p. 12.

Pierson, John. "Screwdriver Redesign Aims to Lock Out Slips," Wall Street Journal. January 22, 1991, pp. 1-2.

Yeaple, Frank. "Zinc's Properties Enhance Hand Tool's Producibility," Design News. January 22, 1990, p. 115.

Lawrence H. Berlow



Also read article about Screwdriver from Wikipedia

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