This invention relates generally to improvements in power tools for use in the installation of threaded fasteners, particularly specialized threaded fasteners of the type used in the aerospace and related industries. More specifically, this invention relates to improvements in a fastener installation tool of the type having a power-driven socket for installing a threaded nut onto a threaded fastener, in combination with a fixture pin for engaging and retaining the threaded fastener against rotation during nut installation.
A variety of specialized fasteners have been developed and are widely used in the aerospace and related industries, wherein these threaded fasteners have been designed to meet specific design criteria and uses. One example of a specialized aerospace fastener comprises a threaded bolt adapted for power-driven installation of a threaded nut, without requiring access to the bolt head. That is, such fasteners are designed to fit through a preformed opening in a substrate or structure with the bolt head inaccessibly disposed at a blind side thereof. A bolt shank protrudes through the substrate opening with a threaded end exposed for screw-on installation of a threaded nut. The shank end is formed to include a small shallow recess of typically hexagonal shape for receiving a mating fixture pin designed to hold the bolt against rotation as the nut is installed. Power-driven installation tools are known for use installing such fasteners, including a small fixture pin disposed coaxially within a power-driven socket for installing the threaded nut while the fixture pin holds the bolt against rotation. One example of such power-driven installation tools is available from United Air Tool, Inc. of Carson City, Nev. under model designation 10185 Series "L" angle head.
In a typical fastener application, using a power-driven installation tool of the type described above, the fixture pin engages and supports the fastener shank, and progressively retracts within the power-driven socket as the threaded nut is advanced onto the fastener shank. At least some friction between the bolt and the substrate assists the fixture pin in retaining the fastener against rotation during nut installation. In recent years, however, particularly with the advent of composite material substrates in aircraft, friction contributes minimally to bolt retention during nut installation, and this is especially true when the substrate opening is coated or lined with a sealant material having a typical low coefficient of friction. Accordingly, on some occasions, the fixture pin is the only structure preventing bolt rotation during nut installation. Torque loads between the power-driven nut and the bolt can sometimes be transmitted directly to the fixture pin, resulting in over-torqueing and breakage of the fixture pin. When this occurs, it has been necessary to remove the installation tool from service for appropriate repair or replacement.
The present invention provides a significant improvement upon fastener installation tools of the type having a fixture pin disposed coaxially within a power-driven socket, wherein the fixture pin is supported by a spring-loaded clutch assembly which permits fixture pin rotation without breakage in response to a torque load exceeding a predetermined limit. The fixture pin is thus protected against breakage during brief time intervals when torque loads applied thereto can be relatively high. In use, the clutch assembly effectively cooperates with the fixture pin to facilitate rapid power-driven nut installation while protecting the tool against breakage.