Box joint employing screw pivot pin for adjustable tightening

An improved box joint for pliers and the like in which the jaw portions are pivotally retained and movable in a prescribed plane normal to a pivot pin, this box joint including:

• (a) a first jaw member that is characterized as having a central tongue portion with outwardly facing surfaces smoothly finished and parallel to the plane of movement;
• (b) a second jaw member with substantially like portions providing first and second outer members and forming the outer sides of a box-like aperture in said second jaw member and with the facing inner surfaces of the aperture finished, and in the assembled condition the outer facing surfaces of the central tongue portion of the first jaw member are in a sliding relationship with the facing inner aperture surfaces of the first and second outer members of the second jaw member;
• (c) a counterbore and a through bore both having a predetermined axis formed in said first outer member of the second jaw and with said counterbore and through bore transverse of the plane of movement of the jaw members;
• (d) a through bore formed in and through the central tongue portion of the first jaw member, said through bore in axial coincidence with said through bore in the first outer member of the second jaw member;
• (d) a pivot pin bushing having a first diameter adapted to be seated in the counterbore of the first outer member and a second reduced outer diameter shank portion sized to be a tight fit in the remaining through bore of this first outer member of the second jaw member and with said shank portion of said bushing entering into said through bore in the portion of the first jaw and providing a pivot for said first jaw member, said pivot pin bushing having an axially threaded bore and in an installed condition is short the inner surface of the second outer member;
• (f) a first counterbore formed in the second outer member of the outer surface of the second member of the second jaw, and a second smaller diameter bore in axial coincidence with this first counterbore and extending through the remainder of the thickness of the second outer member, this counterbore extending toward the central tongue portion sufficiently to establish a thin flexure portion of about one thirty-second of an inch in thickness and sufficiently deflectable for this flexure portion to be moved for tightening the box joint, said second small diameter bore greater in diameter than the through bore sized to receive the pivot pin bushing, said second smaller bore continued into the top surface portion of the central tongue portion of the first jaw member to form a recess, the second smaller bore in the top surface of the central tongue portion of a shallow depth;
• (g) a washer of plastic such as Teflon, Nylon and the like and having anti-friction and cold flow properties, said washer having an outer diameter disposed to enter and be seated in said first counterbore in the second member of the second jaw member, said washer having an inner bore slightly larger than the threaded portion of the pivot pin bushing and with said washer having a thickness about the equivalent of the thin flexure portion, the washer adapted for mounting in said first counterbore before further assembly, and
• (h) a securing screw having a head adapted to seat and move the second outer member flexure portion toward the central tongue, said screw having a shoulder portion immediately below the head and about the thickness of the washer and of a diameter substantially equal to the outer diameter of the pivot pin bushing, the shank and shoulder of the screw in coincidence with the axis of the pivot pin bushing, the thread portion of said securing screw entering into the threaded portion of the pivot pin bushing and with tightening of the screw brings the box joint members into the desired sliding relationship of one to another, this adjustment reducing and/or eliminating any developed and unwanted play of and in the joint, the tightening of the screw causing a cold flow of the washer so as to surround the shoulder portion of the screw and to flow into the second smaller diameter bore in the thin flexure portion and into the shallow recess in the top surface of the tongue portion of the first jaw member, the washer thereby providing an anti-friction bearing.