Flexible shaft plug insert

#The present invention generally relates to hand tools and more particularly to an apparatus for preventing disengagement of an axially moveable and rotatable flexible core member of a flexible shaft attachment of the type which has a handpiece on one end, and its other end is coupled to a rotary hand tool.

#There has been continued innovation and improvement in the design of power tools, particularly rotary hand tools of the type that are used in woodworking, metal working and the like. Examples of such products are those produced under the Dremel brand by the S-B Power Tool Corporation of Chicago, Ill., which also produces many accessory attachments for such rotary hand tools. The rotary hand tools are generally cylindrical in shape and have a motorized drive unit with a rotary output shaft that is adapted to drive the various rotary tools, such as small saw blades, sander discs, grout removal tools and various shaped cutting tool bits. There are also may accessory attachments that can be used in association with the rotary tools, with the accessory attachments being connected to the stationary nose end portion of the rotary tool via a coupling apparatus. Among such accessory attachments is a flexible shaft attachment that conveniently allows the user to operate the various rotary tool bits around corners or in other remote areas of operation.

#While such flexible shaft attachments have been available for many years, the manner in which the flexible shaft attachments are coupled to the tool has been the subject of continuing efforts to provide a simple and effective mechanism for preventing the disengagement of the flexible core member from the handpiece. Thus, the manner in which flexible shaft attachments are presently coupled to rotary tools, while effective, does not prevent disengagement of the flexible core member from the handpiece end under some operating circumstances.

#FIG. 1 is a side elevational view of the assembly in which the stop plug apparatus of the instant invention operates, and illustrates the flexible shaft attachment and rotary tool coupled to one another via the coupling apparatus;

#FIG. 2 is a top view of the assembly illustrated in FIG. 1.

#FIG. 3 is an exploded sectional view of the stop plug apparatus of the instant invention with the coupling apparatus of FIG. 1, taken along the 3-3 line.

#The preferred embodiment of the stop plug apparatus includes a generally cylindrical stop plug having an open end and a closed end, and a cylindrical chamber spanning therebetween, where the open end is configured to receive the flexible core member and the closed end prevents undesirable axial movement of the flexible core member of a flexible shaft into the output shaft of the rotary tool, which often results in disengagement of the flexible core member from the handpiece end.

#Disengagement ordinarily occurs because the output shaft of the motorized drive unit has a predetermined internal depth and circumference, which shaft ordinarily has a collet inserted inside of it and a collet nut threaded on it. However, in applications wherein the output shaft is coupled directly to the flexible shaft attachment, the collet and collet nut are removed and the output shaft and flexible shaft attachment are directly threadedly connected to one another. Therefore, when modest force is applied to the core in the direction of the drive unit, the flexible core member disengages from the handpiece and slides into the output shaft of the rotary tool.

#Alternative methods of preventing disengagement of the core from the handpiece have proven disadvantageous in view of the present invention. For example, lengthening the flexible core to extend between the handpiece and the distal end of the output shaft would necessarily preclude any axial movement between of the flexible core. However, this configuration is disadvantageous for numerous reasons. First, end portions at each end of the flexible core have square cross-sections to facilitate attachment and rotation of the flexible core at its ends. Lengthening the end portion at the driven end would require commensurate lengthening at the handpiece end so that the end portions would be balanced. Lengthening at the handpiece end would result in part of the square end portion at the handpiece end extending past the handpiece, and rotation of the square end portion within the flexible sheath causes undesirable friction. This friction can cause degradation and erosion of the flexible sheath, and unwanted vibrational movement of the square end portion interferes with the rotation of the core.