Technical Support

SMALL-SCREW INSERTION SYSTEMS KEEP PACE
WITH DRIVE FOR PERFORMANCE, PRODUCTIVITY, AND SAFETY

The process of installing small screws into assemblies traditionally has presented challenges on the production line and recently has begun to raise a variety of related workplace issues. When a worker must insert loose screws by hand directly into a workpiece or when each screw must be handled and fed one at a time into conventional semi-automated power fastening tools, productivity rates can fall and associated costs can rise due to the required labor-intensive effort.

Using typical screw-insertion methods, too, there is no assurance that proper seating torque for the small screws will be achieved consistently and accurately and, if a screw is not seated properly, it could loosen and contribute ultimately to end-product hazard or failure.

For the benefit of workers, in general, a growing emphasis on safety and the recognized risks of repetitive motion stress injuries have started to prompt manufacturers to seek small-screw insertion methods that will prevent problems before they can occur. Advances in fastening systems have followed.

Numerous OEM industries, including automotive, communications, and medical, understand that they have a growing stake in resolving the issues linked to the process of installing small screws: the fact is there are so many more metal or plastic applications where small machine screws or thread-cutting and thread-forming screws are now required. These screws continue to be used by companies big and small for attaching printed circuit boards to frames, nameplates to valve and meter housings, sheet metal assemblies, contract assemblies for telecommunications systems, and countless others.

As one example, a manufacturer of gas-powered lawn mowers uses three small screws to secure a die-cast zinc cover to a housing made of thin-gauge sheet metal. The die-casting safeguards the fast-moving, fly-wheel ignition system. Since the system spins at high speed, a loose or missing cover would create a safety hazard for the user. It is crucial in this application for the screws to seat properly and not work loose from the steady vibration caused by the gas-powered engine.

Initially, the screws were inserted in this application by hand, which proved expensive and labor-intensive. The process also raised concerns about the safety of workers' fingers during screw insertion, as well as the risk of repetitive motion stress injuries.

This manufacturer was able to resolve these issues by converting to the StickScrew® System, which has been designed to provide an extremely fast, accurate, and efficient method of small-screw insertion. As the name suggests, this self-contained system consists of a "stick" of up to 110 serially connected, hex-head screws that are driven by a companion lightweight air-powered StickShooterT driver. Since the screws are connected in a "stick," an operator need not handle any loose individual screws, which can yield immediate productivity gains at the outset.

Operation of the system is quick and uncomplicated. A worker inserts the stick in the driver, advances to the second screw, depresses the lever, places the tip of the rotating screw in the hole, and the screw is driven home. The torque-engineered and precision-machined screw twists off cleanly from the stick when precise seating torque is reached. The next screw is automatically indexed into the driving position and ready for insertion.

A clear advantage inherent in this system in preventing over- or under-torquing is the result of proper torque being built into the screw instead of the driver. In fact, the material diameter between each screw determines the seating torque. If, for example, a hole is too large, the correct torque will not be reached and the screw will not twist off. If the hole is too small or improperly threaded, the screw will twist off prematurely and then can be readily identified as defective.

In the application for the lawn-mower cover, concerns relating to torque, as well as end-product integrity, are worries of the past. As for documented productivity, the manufacturer reports that one operator is now doing the work done formerly by three -- with an added bonus that overall production output rates have since climbed. The system has further made potential worker safety issues moot.

In another application example, a major computer manufacturer previously had relied on an electric screwdriver to attach CD-ROMs to the chassis. (The screws fasten the sheet metal "covers" to stamped sheet metal.) This created a time-consuming bottleneck in the production line, and loose screws sometimes dropped into the chassis, which threatened to cause a circuit problem. In addition, the electric screwdriver sometimes would slip off the head of the hand-held screw and cause injury to the assembler's fingers or wrist. The manufacturer's switch to the StickScrew System has realized savings in time and money, more reliable assemblies, enhanced worker confidence, and a safer workplace.

Other StickScrew System benefits cited by users include reduced defects and rework; reduced operator error; easy handling, storage and inventory of screws; elimination of expensive bowl, track or indexing feeders; less waste; easy portability of the driver for use throughout a plant; and elimination of mixed or loose screws. The serially connected screws further effectively replace rivets at one-tenth the cost and can prevent expensive downtime typically experienced with expensive bulk feed/screw drivers that are prone to jam and offer little in the way of quality control for correct seating and tightness (torque).

As part of this system, two ergonomically friendly StickShooter drivers are currently available, and both are designed to eliminate the harsh shocks and turning required with other types of driver tools. Both StickShooter driver models are lightweight, feature a rugged aluminum cast body and precision-machined components, and operate on 90 psi using a 1/4" shop-air line.

The standard In-Line Stickshooter tool weighs 1.4 lbs./.64 kg. and a fingertip throtttle activates the pneumatic motor. An alternative model, the Pistol Grip StickShooter, weighs 2 lbs./.91 kg. and features a 100-degree angle pistol grip design to minimize operator fatigue. The pneumatic motor is activated by a trigger, and this model is especially useful when horizontal assembly is preferred.

Due to a growing number of diverse applications, a wide range of machine screw thread sizes, lengths, and materials have been developed for use in this advanced system.

Standard machine screw thread sizes range from miniature #0-80 through #8-32 and M2 to M3. Screws are available in a variety of materials, including steel, stainless steel, brass, and aluminum. They can be plated, black oxidized, or hardened. All screws can be customized to meet specific application requirements. In addition, other thread types, such as thread-cutting and thread-forming, can be specified.

As a guide in matching application with the system's capabilities, several basic specification decisions for the screws should first be made: type (machine screw, thread cutter, or thread former); size; length; hex size; and material. After these parameters have been established, custom options for the screws can be evaluated and then developed.

These application-specific options for consideration include screw hardness (as machined, case hardened, or bright hardened); plating (black oxide, clear or dichromate zinc, chrome, tin, or anodized); head height (standard, easy access, low profile, or other/special); type of coating (lubrication, thread locking); and torque requirements (low for plastics, medium for standard, or high for steel).

The screws are furnished only with hex heads, which is required by the process of machining the screws in solid lengths from hexagonal bar stock, but three head configurations can be specified depending on application needs: a thick "easy access" head for ease of removal and re-installation; a standard head; or a shallow "tamper proof" head for permanent installation.

As industry strives to gain improved performance, productivity, and safety, the drive has accelerated for advanced yet low-cost production systems -- including those required for basic fastening. The StickScrew System represents one example of how far technology has progressed in supporting the evolving requirements.

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