GB2495013A

GB2495013A - A shearing hand piece tension lock ring

Info

Publication number: GB2495013A
Application number: GB1220116.6A
Authority: GB
Inventors: Robin James Howell; John Alun Harris Williams
Original assignee: Lister Shearing Equipment Ltd
Current assignee: Lister Shearing Equipment Ltd
Priority date: 2012-11-05
Filing date: 2012-11-08
Publication date: 2013-03-27
Anticipated expiration: 2032-11-08
Also published as: GB201220116D0; GB201219860D0; GB2495013B

Abstract

A shearing hand piece tension lock ring 86 is formed from a resilient material having a generally circular cross-sectional shape and describing an arc of approximately 340 degrees. The tension lock ring 86 has a first end 74 configured to fit a recess (60, fig. 3a) of a shearing hand piece tubular bush (42, fig. 3a). The tension lock ring 86 has a second end 76 having a radially outwardly positioned rounded shoulder 88 and an end face 82 that faces the interior of the tension lock ring 86. The end face 82 is formed by cutting diagonally through a bend (90, fig. 5c) formed in the tension lock ring 86. The end face has the shape of an oval with a single axis of symmetry 94 (see fig. 6), or a truncated oval with a single axis of symmetry (see figures 7 & 8). The finishing of the second end 74 lessens the risk of snagging between the end of the tension lock ring and the interior of the shearing hand piece tensioning cap (46, fig. 1), and also lessens the risk of injury to an operator during assembly or servicing of the shearing hand piece.

Description

improvements in or Relating to Shearing Hand Pieces The present invention relates to shearing hand pieces and in particular to an improved tension lock ring for a shearing hand piece. The invention further relates to a shearing hand piece having an improved tension lock ring.

A shearing handpiccc typically includes a hand piece body having a crank spindle which drives a crank pin. The crank pin, in turn, drives a fork assembly which converts the rotational motion of the crank pin into reciprocal lateral motion. A cutter is connected to the fork assembly which, in use, moves ovcr a fixed comb fitted to the hand piece body. For optimum interaction between the cutter and the comb, an operator must accurately set the pressure applied by the cufter to the comb. This is achieved by providing an adjustment mechanism which is operable to pivot the fork assembly towards and away from the comb. The adjustment mechanism includes a tension lock ring which prevents the adjustment mechanism from loosening when the hand piece is used.

According to a first aspect of the present invention there is provided a shearing hand piece tension lock ring, the tension lock ring being formed from a resilient material having a generally circular cross-sectional shape and describing an arc of approximately 340 degrees, the tension lock ring having a first end configured to fit to a rcccss of a shearing hand piece tubular bush, whcrcin the tension lock ring has a second end having a radially outwardly positioned rounded shoulder and an end face that faces the interior of the tension lock ring, wherein the endface is formed by cutting diagonally through a bend formed in the tension lock ring, and wherein further the end face has the shape of either an oval with a single axis of symmetry or a truncated oval with a single axis of symmetry.

According to a second aspect of the present invention there is provided a method of manufacturing a shearing hand piece tension lock ring, the tension lock ring being formed from a rcsilicnt material having a generally circular cross-scctional shape and describing an arc of approximately 340 degrees, the tension lock ring having a first end configured to fit to a recess of a shearing hand piece tubular bush, wherein the tension lock ring has a second end having a radially outwardly positioned rounded shoulder and an end face that faces the interior of the tension lock ring, wherein the second end of the tension lock ring is formed by bending the second end though an angle of greater than 90 degrees and less than 180 degrees, and then cutting diagonally through the bend where the start of the cut coincides with the start of the bend on the inner side of the bend so as to form an end face having the shape of either an oval with a single axis of symmetry or a truncated oval with a single axis of symmetry.

By bending and then cutting the ring in the manner described, a ring is formed which has a rounded shoulder which is positioned radially outwardly of any sharp edges that may be present on the end face. Potential problems with snagging of such sharp edges are thus avoided.

According to a third aspect of the present invention there is provided a shearing hand piece having a tension lock ring according to the first aspect.

An embodiment of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 shows a cross sectional view of a shearing hand piece; Figure 2 shows a cross sectional view of the tension nut of the shearing hand piece; Figure 3a shows a perspective view of the tubular bush of the shearing hand piece; Figure 3b shows a side view of the tubular bush; Figure 3c shows a cross sectional view of the tubular bush; Figure 4a shows a perspective view of a conventional tension lock ring Figure 4b shows a plan view of the tension lock ring of figure 4a; Figure Sa shows a perspective view of a tension lock ring according to the present invention; Figure Sb shows a plan view of the tension lock ring of figure 5a; Figure Sc shows an enlarged view of one end of the tension lock ring of figure S a; Figure 6 shows a further view of one end of the tension lock ring of figure 5a; Figure 7 shows the shape of the end superimposed on the cross-sectional shape of the material forming the tension lock ring; and Figure 8 shows a further view of one end of the tension lock ring of figure Sa.

Figure 1 shows a cross-sectional view of a shearing hand piece generally designated 10. The hand piece 10 includes a body 12 within which there is rotatably mounted a crank spindle 14. The crank spindle 14 is provided with a crank pin 16 which is offset with respect to the longitudinal axis of the crank spindle 14. The crank pin 16 is received in a slot 18 of a fork assembly 20 which extends out of an opening 22 in a forward end of the body 12. The fork assembly 20 is mounted to a thlcrum post 24 of the body 12 such that rotary motion of the crank spindle 14 and crank pin 16 is translated to reciprocating pivoting motion of the fork assembly 20 about tbe fulcrum post 24. The fork assembly 20 is retained in association with the fulcrum post 24 by a fork retaining screw 26 of the body 12.

In use, the shearing hand piece 10 is provided with a comb and a cutter, both not shown. The comb is fixed to the body 12 by comb retaining screws 28. The cutter rests on the comb and is provided between the comb and the forward end 30 of the fork assembly 20. The cutter is provided with a plurality of apertures or recesses which receive corresponding projections 32 provided on the underside of the fork assembly forward end 30. The cutter is not fixed to the fork assembly 20, but instead is maintained in association with the fork assembly 20 by the spacing of the fork assembly 20 relative to the comb.

In order for the comb and cutter to operate correctly, an operator is required to accurately set the force that is applied to the cutter by the fork assembly 20. This is achieved by the provision of an adjustment mechanism, generally designated 34, which is provided at the forward end of the body 12. The adjustment mechanism 34 includes a tension pin 36 which extends between a recess 38 of the fork assembly 20 and a sleeve 40 of the adjustment mechanism 34. The sleeve 40 is slidably mounted within a tubular bush 42 which is mounted to a through aperture 44 of the body 12.

The tubular bush 42 is surmounted by a cap 46 which, in use, is manipulable to move the sleeve 40 and tension pin 36 and thereby adjust the force applied by the fork assembly 20 to the cutter.

Figures 2 to 3c show the tubular bush 42 and cap 46 in greater detail. The bush 42 has a substantially tubular body 48. The body 48 has an upper threaded portion 50 and a lower threaded portion 52. The threadform of the lower threaded portion 52 is coarser than the threadform of the upper threaded portion 50. The lower threaded portion 52 is provided so as to enable the tubular bush 42 to be engaged with a complementarily threaded portion of the body through aperture 44. The upper threaded portion 50, as will be described in greater detail below, cooperates with a complenientarily threaded portion of the cap 46.

Located between the upper and lower threaded portions 50,52 of the tubular bush 42 there is provided an annular projection 54. The projection 54 is provided with an annular recess 56 which, in use, defines a seat for a tension lock ring 57. The annular projection 54 is provided with a cut out 58 which is aligned with a hole 60 which extends through the wall of the tubular body 48 of the bush 42. The cut out 58 and hole 60, in use, are used to locate and retain the tension lock ring 57 relative to the annular recess 56.

The cap 46 includes an interior 62 defined by a substantially circu'ar end wall 64 and a peripheral side wall 66. The interior 62 comprises a portion 68 proximal to the endwall 64 having a first diameter and a portion 70 distal to the endwall 64 having a second diameter. The second diameter is greater than the first diameter. The portion 68 of the cap interior 62 proximal to the endwall 64 is threaded 72 and enables the cap 46 to be connected to the upper threaded portion 50 of the tubular bush 42. As can be seen from figure 1, when the cap 46 is threadably engaged with the upper threaded portion 50 of the bush 42 the portion 70 of the cap 46 which is distal to the end wall 64 surrounds the annular projection 54 of the bush 42 and the tension lock ring 57.

A conventional tcnsion lock ring 57 is shown in figures 4a and 4b. The ring 57 is generally circular when viewed in plan having a centre X. The ring 57 formed from a length of spring steel having a substantially circular cross-section along its length. A first end 74 of the ring 57 is bent through approximat&y 90 degrees such that it is aligned radially with respect to the ring centre X. The second end 76 of the ring 57 is not bent towards the ring centre X. The ring 57 describes an arc of approximately 340 degrees and thus an opening 78 is provided between the first aad second ends 74,76.

The end face 80 of the first end 74 of the ring 57 faces to the interior of the ring 57 in a radial direction. The end face 82 of the second end 76 of the ring 57 faces to the exterior of the ring 57 in a tangential direction.

The outer diameter of the ring 57 is greater than the inner diameter of the distal portion 70 of the cap 46. The inner diameter of the ringS? is greater than the smallest diameter of tubular bush annular recess 56, but less than the largest diameter of the tubular bush projection 54.

In use, the ring 57 is fitted to the tubular bush 42 such that first end 74 of the ring 57 is received in the hole 60 of the bush 42 and the remainder of the ring 57 is received loosely in the tubular bush annular recess 56. When the cap 46 is fitted to the tubular bush 42 it will be understood that the portion 70 of the end cap 46 distal to the endwall 64 compresses the ring 57 into the recess 56. Due to the relative diameters of the recess 56, ringS? and portion 70 of the end cap 46 distal to the endwall 64 it will be understood that, with the threaded portions 50,72 engaged, clockwise rotation of the cap 46 results in slight momentary compression of the ring 57 into the recess 56. This results in a reduction in the resistive force applied by the ring 57 to the cap 46. The portion 70 of the end cap 46 which is distal to endwall 64 is not tapered, and thus the reduction in resistive force is constant and does not decrease further with continued clockwise rotation of the cap 46. Conversely, counter clockwise rotation of the cap resuhs in slight momentary expansion of the ring 57. This results in an increase in the resistive force applied by the ring 57 to the cap 46.

The reduction in resistive force applied in the clockwise direction permits an experienced operator to "feel" and thus accurately set the pressure applied to the comb by the cutter. The increase in resistive force in the counter clockwise direction prevents the cap 46 loosening in use.

A problem with the ring 57 shown in figures 4a and 4b is that the second end 76 is provided with a radially outwardly positioned sharp shoulder 84 which rests against the inner surface of the cap 46. This shoulder 84 can interfere with the smooth clockwise and counter clockwise rotation of the cap 46 by an operator when setting the cutter pressure by snagging or catching on the interior of the cap 46, and thus preventing the operator from accurately setting a desired cutter pressure.

Figures Sa to Sc show a tension lock ring generally designated 86 according to the present invention. Features common to the ring 57 described with reference to figures 4a and 4b are identified with like reference numerals. As before, the ring 86 has a first end 74 which is configured to fit to the through hole of a tubular bush. The ring 86 further defines an arc of approximately 340 degrees. The ring 86 differs in that the radially outwardly positioned shoulder 88 of the second end 76 is now rounded. Also, the end face 82 of the second end 76 faces to the interior of the ring 86. The rounded shoulder 88 alleviates the snagging and catching problems of the sharp shoulder 84.

The rounded shoulder 88 is positioned radially outwardly of the end face 82 and thus the edges of the end face 82, in use, is prevented from contacting the interior of the cap 46.

The second end 76 of the ring 86 is formed by first bending the end of the ring through an angle of greater than 90 degrees but less than 180 degrees to produce a bend 90 and then cutting diagonally through the bend 90 with the start of the cut coinciding with the start 92 of the bend 90 on the inner side of the bend 90. This results in an end face 82 of the second end 76 which faces the interior of the ring 86.

Figures 6 and 7 show the end face 82 of the second end 76 in greater detail. As the end face 82 is produced by cutting diagonally through a bend formed in the ring 86, the end face 82 has an oval shape which is similar to that of a teardrop or an egg.

More specifically, the end face 82 has the shape of an oval with a single axis of symmetry 94. Figure 6 shows the shape of the end face 82 superimposed upon the circular cross-sectional shape of the remainder of the ring 86. The shortest or minor diameter of the oval end face 82 is equal to the diameter of the remainder of the ring 86. Figures 6 and 7 show the shape of the end face 82 resulting from a diagonal cut being made filly through a bend 90. The resuhing sharp tip present on the radially outer edge of the end face 82 may subsequently be filed, ground or otherwise finished at an angle to the plane of the end face 82 so as form a truncated oval end face 82 having a single axis of symmetry 94. Such filing or grinding results in a secondary face 98 that intersects the plane of the end face 82 at broken line 96 It will be appreciated that removal of the sharp tip reduces the possibility of injury during assembly or subsequent servicing of the shearing hand piece to which the lock ring 86 is fitted. A side view of the second end 76 having such a secondary face 98 is shown in figure 8.

As an alternative, a diagonal cut may be made partially through the bend 90 and followed by the unwanted end of the ring 86 being snapped or otherwise broken off as indicated by broken line 96. The resulting sharp tip present on the radially outer edge of the end face 82 may subsequently be filed, ground or otherwise finished at an angle to the plane of the end face 82 so as form a truncated oval end face 82 having a single axis of symmetry 94. As noted above, the filing or grinding of the sharp tip results in a secondary face 98 that intersects the plane of the end face 82. It will be appreciated that removal of the sharp tip reduces the possibility of injury during assembly or subsequent servicing of the shearing hand piece to which the lock ring 86 is fitted.

The tension ock ring 86 of the present invention may be manufactured from spring steel having a diameter of approximately 1.4mm.

Claims

<claim-text>Claims 1. A shearing hand piece tension lock ring, the tension lock ring being formed from a resilient material having a generally circular cross-sectional shape and describing an arc of approximately 340 degrees, the tension lock ring having a first end configured to fit to a recess of a shearing hand piece tubular bush, wherein the tension lock ring has a second end having a radially outwardly positioned rounded shoulder and an end face that faces the interior of the tension lock ring, wherein the endfaee is formed by cutting diagonally through a bend formed in the tension lock ring, and wherein further the end face has the shape of either an oval with a single axis of symmetry or a truncated oval with a single axis of symmetry.</claim-text> <claim-text>
2. A method of manufacturing a shearing hand piece tension lock ring, the tension lock ring being formed from a resilient material having a generally circular cross-sectional shape and describing an arc of approximately 340 degrees, the tension lock ring having a first end configured to fit to a recess of a shearing band piece tubular bush, wherein the tension lock ring has a second end having a radially outwardly positioned rounded shoulder and an end face that faces the interior of the tension lock ring, wherein the second end of the tension lock ring is formed by bending the second end though an angle of greater than 90 degrees and less than 180 degrees, and then cutting diagonally through the bend where the start of the cut coincides with the start of the bend on the inner side of the bend so as to form an end face having the shape of either an oval with a single axis of symmetry or a truncated oval with a single axis of symmetry.</claim-text> <claim-text>
3. A shearing hand piece having a tension lock ring as claimed in claim I.
4. A shearing hand piece tension lock ring substantially as hereinbefore described with reference to or as shown in figures 5a to 7.
5. A shearing hand piece having a tension lock ring substantially as hereinbefore described with reference to or as shown in figures 5a to 7.</claim-text>