Robust bumper spring assembly

1. A. bumper spring assembly, comprising:

a one piece mandrel having a head end and a tail end, an integral head piece at its head end, and a concentric bore formed in the tail end that further includes an external thread surrounding the tail end;

a bumper spring configured as a coil spring disposed concentrically on the mandrel, a first end thereof adjacent the head end;

a bumper spring cage disposed concentrically on the mandrel adjacent a second opposite end of the bumper spring; and

a cage nut, having an internal screw thread terminated by an outward-directed chamfer near the distal end of the cage nut, threaded onto the external screw thread of the tail end of the mandrel thereby securing the bumper spring and the bumper spring cage between the head end of the mandrel and the cage nut; wherein further

a distal portion of the tail end of the mandrel is expanded outward in a cold forming process against the threads in the cage nut next to the outward chamfer to lock the threads of the cage nut to the tail end of the mandrel without the use of pins or set screws.

2. The assembly of claim 1 , wherein the outward expansion of the distal portion of the tail end of the mandrel deforms the endmost screw threads of the cage nut and the tail end of the mandrel proximate the outward-directed chamfer.

3. The assembly of Claim 1 , wherein the headpiece comprises a solid cylindrical member configured with a fishing neck at a first end and a stabilizing body at a second end wherein the stabilizing body includes longitudinal stabilizing ridges, concentric flow reliefs, and chamferred edges.

4. The assembly of claim 3 , wherein the longitudinal stabilizing ridges comprise a plurality of longitudinal strips of the outermost diameter of the stabilizing body alternately disposed between the longitudinal undercuts.

5. The assembly of claim 3 , wherein the concentric flow reliefs comprise a plurality of longitudinal undercuts in the outermost diameter of the stabilizing body, alternately disposed with the longitudinal stabilizing ridges around the circumference of the stabilizing body.

6. The assembly of claim 5 , wherein the longitudinal undercuts are of substantially equal dimensions.

7. The assembly of claim 5 , wherein the longitudinal undercuts are flat.

8. The assembly of claim 5 , wherein the longitudinal undercuts are curved in a concave direction.

9. The assembly of claim 3 , wherein the chamferred edges comprise inward-rounded edges of the outermost diameter of the stabilizing body proximate the first end of the bumper spring.

10. The assembly of claim 1 , wherein the bumper spring comprises a coil spring formed of wire and haying a uniform pitch.

11. The assembly of claim 10 , wherein the bumper spring comprises a coil spring formed with closed and ground ends.

12. The assembly of claim 1 , wherein the bumper spring cage is a hollow cylindrical member comprising one or more of the following features selected from the group consisting of flow ports, relieved channels, and egress sweeps.

13. The assembly of claim 12 , wherein the flow ports comprise at least two elongated openings through a wall of the hollow cylindrical member and separated by substantially equal intervals around the circumference of the bumper spring cage.

14. A mandrel for a bumper spring assembly, comprising:

a one piece mandrel having a head end and a tail end, an integral head piece disposed at its head end, and a concentric bore formed in the tail end that further includes an external thread surrounding the tail end; and

a cage nut having an internal screw thread is threaded onto the external screw thread of the tail end of the mandrel for securing a bumper spring and a bumper spring cage between the head end of the mandrel and the cage nut; wherein further

a distal portion of the tail end of the mandrel is swaged during a cold forming process to lock the cage nut to the tail end of the mandrel without the use of pins or set screws.

15. The mandrel of claim 14 , wherein the swaged distal portion of the tail end of the mandrel is flared against the cage nut.

16. The mandrel of claim 14 , wherein the integral headpiece comprises:

a solid cylindrical body having first and second ends and a fishing neck disposed at the first end thereof;

a stabilizing body disposed at the second end of the headpiece and having a plurality of stabilizer ridges disposed around a full diameter thereof; wherein

the stabilizing body includes a plurality of undercut reliefs disposed in alternating relationship with the stabilizer ridges around the circumference of the headpiece and parallel to a longitudinal axis of the headpiece; and

a taper or chamfer around edges of the stabilizing body proximate the second end of the head piece.

17. A bumper spring cage for use with the mandrel of claim 14 , comprising:

a hollow cylindrical member having a plurality of elongated flow ports formed between an inside bore and an outer surface of the hollow cylindrical member; wherein

the elongated flow ports are uniformly disposed around the circumference of the hollow cylindrical member.

18. The bumper spring cage of claim 17 , wherein further comprising:

a plurality of exit channels connecting the elongated flow ports with the outer diameter of the cage; wherein

the exit channels are fluted with a plurality of longitudinal grooves along the length thereof.

19. A bumper spring for use with the mandrel of claim 14 , comprising a coil spring disposed concentrically on the mandrel, a first end of the coil spring adjacent the headpiece.

20. The bumper spring of claim 19 , wherein the coil spring comprises a wire, having a uniform pitch, and having closed and ground ends thereof.