Captive thread forming terminal screw

• US 4,261,402 A
• Filed: 11/06/1978
• Issued: 04/14/1981
• Est. Priority Date: 11/06/1978
• Status: Expired due to Term

• Current Assignee: Textron Inc
• Original Assignee: Textron Inc
• Inventors: Stanaitis, Peter P.
• Primary Examiner(s): Britts, Ramon S.
• Application Number:
  US05/958,142
• Time in Patent Office: 890 Days
• Field of Search: 151/69, 151/37, 151/35, 151/22, 85/1 P, 85/1 K, 85/46, 339/269, 339/272 R, 339/263 R, 339/246
• US Class Current: 411/107
• CPC Class Codes: F16B 35/044 Specially-shaped ends
• CPC Class Codes: F16B 41/002 Measures against loss of bolts, nuts or pins devices for fastening nuts to surfaces F16B37/04
• CPC Class Codes: H01R 4/301 having means for preventing complete unscrewing of screw or nut
• CPC Class Codes: Y10S 411/999 with retainer, e.g. tether

Abstract

A self-tapping, self-captivating fastener is provided for engagement in a predrilled aperture to enable the connection of an electrically conductive element such as a lead wire, or spade type terminal attached to the end of such a wire, to a workpiece or bus bar. The fastener includes a shank and an enlarged driving head, said shank having a threaded portion which includes a thread lead-in portion that tapers and converges in a direction away from the driving head toward an enlarged abutment projection formed at the work entering end of said fastener. The diameter of this abutment projection is less than the diameter of the predrilled aperture and said apertural diameter is less than the crest diameter of the threaded portion. Thus the abutment portion may pass through this aperture with said threaded portion reshaping the periphery of the aperture to form internal mating threads, such that the apertural diameter is reduced to less than that of the abutment portion. Accordingly, upon withdrawal of the thread, said abutment portion will impinge upon the internal threads thereby rendering said fastener captive. In addition, the convergence of said thread lead-in portion is such that when said abutment portion impinges the internal threads, the thread turns upon the lead-in portion are not in contact with said internal thread whereby continued rotation of the fastener will not damage the internal threads.

Claims

1. In combination, a self-tapping, self-captivating fastener member and a relatively thin workpiece having a pre-drilled aperture of predetermined size formed therein, said fastener member including a driving head and an elongate shank extending from said driving head, said shank having a threaded portion formed thereon, said threaded portion including a plurality of thread-forming turns adapted to form an internal mating thread on said aperture wall upon engagement of the fastener member in said aperture, and a thread lead-in portion which includes one or more incomplete or underfilled thread turns, said thread lead-in portion being tapered and converging in a direction away from said driving head and of a length greater than the depth of the pre-drilled aperture, and an enlarged abutment portion formed on said shank adjacent the terminus of said lead-in portion, and having a maximum diameter which is greater than the minimum diameter of said thread lead-in portion, and also greater than the crest diameter of the mating internal thread to be formed by said thread-forming turns, whereby upon assembly of said fastener member with said workpiece, said abutment portion may pass through said aperture with said thread-forming turn reshaping said aperture periphery to form said internal mating thread, such that upon attempted removal of said fastener, said abutment portion will engage said internal threads thereby rendering said fastener captive with respect to said workpiece, and further due to the lead-in portion being of a length greater than the depth of said pre-drilled aperture, the convergence of said thread lead-in portion and the incomplete thread turns thereon when said abutment portion engages said internal thread, the thread turns on said lead-in portion proximate said internal thread will be of insufficient crest height to effect mating, driving engagement with said internal thread, such that continued rotation of the fastener member will not result in withdrawal of the fastener from the aperture and damage to said internal thread which would result from said abutment portion passing through said internally threaded aperture.

3. The combination according to claim 1 or claim 2, wherein said shank includes an unthreaded portion intermediate said threaded portion and said driving head, and there is further provided a washer member carried on said unthreaded portion, said washer member being maintained captive on said shank by said thread turns and said driving head.

4. The combination according to claim 1 or claim 2, wherein said enlarged abutment portion includes a tapered section extending from the terminus of said lead-in portion, said tapered section diverging in a direction away from said driving head.

5. The combination according to claim 4, wherein said abutment portion further includes a cylindrical section extending axially of said tapered section, and said abutment portion defines the work-entering end portion of said fastener member.

6. The combination according to claim 1 or claim 2, wherein said thread lead-in portion is formed on a shank section which also converges in a direction away from said driving head, with the thread on said lead-in portion running out at a location spaced axially from said enlarged abutment portion.

7. The combination according to claim 1 or claim 2, wherein said thread-forming turns are of a multi-lobular configuration.

2. In combination, a self-tapping, self-captivating fastener member and a relatively thin workpiece having a pre-drilled aperture of predetermined size formed therein, said fastener member including;

a driving head, an elongated shank extending from said driving head, said shank having formed thereon a threaded portion and an abutment portion disposed adjacent said threaded portion, said threaded portion including a thread lead-in portion and a plurality of thread-forming turns of a size and configuration to engage said aperture periphery and form a mating internal thread thereon, said abutment portion being sized such that the maximum diameter thereof is less than the diameter of said aperture but greater than the crest diameter of the internal threads to be formed thereon, whereby upon assembly, said abutment portion will pass through said aperture but subsequent to the formation of said internal thread, said fastener member cannot be disassembled since the internal thread will preclude said abutment portion from passing out of said aperture, the improvement wherein, said thread lead-in portion is tapered and converges in a direction away from said driving head, terminating at its minimum diameter section adjacent said abutment portion, with the thread turns on said lead-in portion being incomplete or underfilled, the spacing of said abutment portion from said lead-in portion and the length of said lead-in portion having a combined axial extent greater than the depth of said aperture, such that when said abutment portion engages said workpiece upon attempted withdrawal of said fastener member, only said incomplete, underfilled thread turns of the lead-in portion will be disposed proximate said internal thread, with none of the thread forming turns being in mating engagement therewith, said lead-in portion thread turns being of insufficient height to effect mating, driving engagement with said internal thread, such that continued rotation of said fastener member will not result in withdrawal of the fastener and damage to said internal thread, as would result from said abutment portion passing through said aperture.

8. In combination, a self-tapping, self-captivating fastener member, and a relatively thin workpiece having an aperture formed therein to a predetermined size, said fastener member including a driving head and an elongate shank extending from said driving head, said shank having a threaded portion formed thereon, said threaded portion including a plurality of thread-forming turns adapted to form an internal mating thread on said aperture periphery upon engagement of the fastener member with said workpiece, and a thread lead-in portion which includes one or more incomplete or underfilled thread turns, said thread lead-in portion being tapered and converging in a direction away from said driving head, and an enlarged abutment portion formed on said shank adjacent the terminus of said lead-in portion, and having a maximum diameter which is less than that of said workpiece aperture, but greater than the minimum diameter of said thread lead-in portion, and also greater than the crest diameter of the mating internal thread to be formed by said thread-forming turns, whereby upon assembly of said fastener member with said workpiece, said abutment portion may pass through said aperture with said thread forming turns reshaping said aperture periphery to form said internal mating threads the spacing of said abutment portion from said lead-in portion and the length of said lead-in portion having a combined axial extent greater than the depth of said aperture, such that when said abutment portion engages said workpiece upon attempted withdrawal of said fastener member, only said incomplete, underfilled thread turns of the lead-in portion will be disposed proximate said internal thread, with none of the thread forming turns being in mating engagement therewith, said lead-in portion thread turns being of insufficient height to effect mating, driving engagement with said internal thread, such that continued rotation of said fastener member will not result in withdrawal of the fastener and damage to said internal thread, as would result from said abutment portion passing through said aperture.

9. The combination according to claim 8 wherein the thread on said lead-in portion runs out at a location spaced axially from said enlarged abutment portion.

10. The combination according to claim 8, wherein said thread-forming turns are of a multi-lobular configuration.

11. A self-tapping, self-captivating terminal fastener member for engagement in a pre-drilled aperture of predetermined size formed in a relatively thin workpiece wherein said fastener upon assembly will provide a captive terminal connection, said fastener member including:

a driving head, an elongate shank extending from said driving head, said shank having thereon a threaded portion and an abutment portion on the work entering, free end of said shank, said threaded portion including a thread lead-in portion and a thread forming portion said thread forming portion comprising a plurality of thread turns of a size and configuration to engage said aperture periphery and form a mating internal thread thereon, said thread lead-in portion including a tapered shank segment which converges in a direction toward said fastener work entering end and terminating at its minimum diameter section adjacent said abutment portion a thread formed on said tapered shank segment of said lead-in portion, the crest diameter of said thread decreasing in height and thereby tapering in the same direction as said shank segment and at least the last thread turn on said thread lead-in portion being incomplete or underfilled and having a crest diameter that is less than the crest diameter of the internal thread to be formed, as determined by the dimensions of said threads on the thread forming portion, said abutment portion being spaced from the terminus of said incomplete or underfilled thread turn on the lead-in portion and sized such that the maximum diameter thereof is less than the diameter of said pre-drilled aperture in the workpiece, but greater than the crest diameter of the internal thread to be formed on said workpiece, as determined by the dimensions of said thread turns on the thread forming portion, such that upon initial assembly, said abutment portion will pass through said pre-drilled aperture, but subsequent to the formation of the internal threads said fastener member cannot be disassembled since the internal threads will have a crest diameter less than the diameter of said abutment portion and will thus preclude said abutment portion from passing out of said aperture, the spacing of said abutment portion from said terminus of the thread turn on said lead-in portion, and the length of said thread on the lead-in portion that is of lesser diameter than the crest diameter of said internal thread being selected to be greater than the normal thickness of workpieces to be employed in conjunction with a captive terminal fastener, such that when said fastener member is retracted and said abutment portion engages said workpiece upon attempted withdrawal of said fastener, only the portion of the terminus of said thread having a crest diameter less than the crest diameter of the internal thread will be disposed proximate said internal thread formed on the workpiece, and therefore none of the thread turns on said fastener will be in mating, driving engagement with said internal thread, such that continued rotation of said fastener member will merely result in spinning of the fastener relative to the workpiece, and will not produce withdrawal of the fastener abutment portion through said internally threaded aperture, which would damage the internal thread previously formed thereon.