GB2182503A - Co-axial cable stripping tool - Google Patents

Abstract

A tool 10 for preparing the end portion of a coaxial cable has a blade 37 which may pivot between two limiting positions, in one of which the cutting edge 38 of the blade lies across a cable-receiving opening 22 to a greater extent than in the other of which positions. On inserting the co-axial cable through the opening 22 and rotating the tool 10 around the cable in one sense, the blade is caused to move to one limiting position so effecting one depth of cut, but on rotating the tool in the other sense around the cable, the blade is caused to move to the other limiting position so effecting a different depth of cut. In this way the different layers of the cable may be severed and removed. <IMAGE>

Description

SPECIFICATION Co-axial cable stripping tool This invention relates to a tool suitable for preparing the end portion of an elongate member having a core and at least three layers therearound, by stripping the layers back successively to expose the core and layers from the end of the member. In particular, but not exclusively, the invention relates to a tool specifically intended to assist the preparation of the end portion of an electric co-axial cable to permit the electrical termination thereof, for example by a jointing technique or by attachment thereto of a co-axial cable connector.

A typical electric co-axial cable has three layers around a central conducting corenamely, an insulating first layer, a conducting layer and an insulating third layer or an outer sheath. Any of these layers may be formed as a group of two or more distinct sublayers-for example, the conducting second layer may comprise a first sub-layer of copper foil wrapped around the insulating first layer and a second sub-layer of braided copper strands laid over the copper foil; and the insulating third layer may comprise two or more sub-layers in order to impart to the completed cable the required electrical and mechanical properties.The invention is of course applicable to such multi-layered cables, and a reference hereinafter to any particular layer of a cable is intended to apply equally to a group of layers, where such a group serves the function of a single layer and so should be removed as a single layer when preparing the end portion of the cable.

Though the tool of this invention may be used to strip layers from multi-layered elongate members other than electric co-axiai cables, it will in the following be described with specific reference to electric co-axial cables. However, it will be appreciated that the tool does have other applications-for instance, the preparation of end portions of fibre optic cables-and the term "co-axial cable" as used herein should be construed accordingly.

The stripping of the end portion of an electric co-axial cable to prepare it ready for termination presents considerably greater problems than those encountered in preparing a conventional single conductor wire. In a manufacturing concern, such problems may be overcome by appropriate automated machinery which is both complex and relatively expensive. However, for on-site installation of coaxial cables, or for relatively small scale users of such cables, the use of automated machinery is not appropriate and to the preparation of an end portion of a co-axial cable can present certain problems. The usual manual method of preparing the end portion of a coaxial cable is by using a sharp hand-held knife-and with some experience, an operator may prepare the end portion of a co-axial cable with complete satisfaction.This action may be assisted with a wire stripper, perhaps especially adapted to the cable to be prepared. Nevertheless, the preparation of the cable still takes some considerable time, and quite often the conductors are accidentally "nicked" by the knife being used to remove the insulation. Also, the operator may inflict a serious wound on himself, by using an open sharp knife blade to perform the actions firstly of removing a relatively long length of outer insulation from the co-axial cable, and subsequently removing a shorter length of outer conductor and inner insulator.

It is an object of this invention to provide a tool suitable for preparing the end portion of an elongate multi-layer member and specifically an electric co-axial cable, which tool is very simple to use and yet is able reliably and consistently to cut selectively through either only an outer layer (e.g. the outer insulating layer of a co-axial cable) or more than just the outer layer (e.g. the outer insulating layer the outer conductor and the inner insulating layer of a co-axial cable, without also cutting the inner conductor).

According to this invention, there is provided a tool suitable for stripping distinct layers from a multi-layer elongate member, which tool comprises a body defining an opening in which may be received the member to be stripped, and a cutting blade pivotally mounted with respect to the body and movable between the two limiting positions in the first of which the cutting edge of the blade projects to a relatively large extent into the opening and in the second of which the cutting edge projects to a relatively lesser extent into the opening, whereby following the location of a multi-layer member in the opening and rotating the tool around the member in one sense, the blade is caused to move to one limiting position such that the cutting edge substantially severs several layers of the member, but on rotating the tool around the member in the other sense the cutting blade is caused automatically to move to its other limiting position such that the cutting edge severs fewer layers of the member.

The following further description of this invention will refer exclusively to electric co-axial cables, though it will be appreciated that many of the preferred features are applicable to tools intended for use with other elongate multi-layer members.

When the tool of this invention is to be used with a co-axial cable, it must specifically be designed to match the cable configuration-but since such cables come in a relatively few number of sizes, this need not present a significant disadvantage. The arrangement of the tool is such that when it is de sired to expose the inner conductor of a coaxial cable, the tool is suitably positioned on the cable and is rotated therearound in one sense, whereby frictional drag on the blade causes the blade to move to its first limiting position and so severing all the layers over the core conductor though the layer immediately overlying the core may only partially be severed radially.Then the tool is again suitably positioned on the cable at the point where the outer conductor is to be exposed, and the tool is moved therearound in the opposite sense, so causing the blade to move to its other position where the cutting edge severs only the outer insulating layer. Stripping of the severed alyers may thereafter easily be accomplished.

Configuring of the tool to suit a particular cable enables the tool to be used successively to expose the core and each overlying layer of the cable, even though the tool effects only two different depths of cut. This is obtained by having the deeper cut only partially severing the insulating first layer of the cable, over the core. A first deep cut is made adjacent the end of the cable by rotating the tool around the cable in the appropriate sense, whereafter the severed outer layers are rotated around the core with respect to the remainder of the cable, so completely separating the first layer whilst leaving the core intact.

The tool is then moved further on the cable, and a second deep cut made. Next the tool is moved yet further on the cable and a third cut made, but this time by rotating the tool in the opposite sense so causing the blade to move to its other position and so effecting a shallow cut through the outer layer only. Preparation is completed by pulling the tool off the cable whilst leaving the blade in the third cut, which action slides the severed layers off the end portion of the cable, so successively exposing the conducting second layer, the first insulating layer and the conducting core.

The above-described method is described in greater detail and also claimed in my co-pending British Patent Application Serial No.

2,153,158 (Application No. 85-01339), filed 18th January, 1985 and entitled "Co-axial Cable End Portion Preparation".

Preferably, the cutting blade is pivotally mounted on a carrier itself slidably mounted with respect to the body, whereby the blade may be moved clear of the opening by sliding movement of the carrier so facilitating the insertion of a cable into the opening. For such an arrangement, the opening may be in the form of a through-bore, in which the cable may be received. Advantageously, a resilient bias is provided between the carrier and body, to urge the blade towards the opening. This enables the blade progressively to penetrate the cable to the required depth as the tool is rotated around the cable.

The blade conveniently has a mounting hole by means of which the blade is pivoted to a pin provided on the tool body (or carrier, if provided). The blade may then have a second hole, preferably in the form of an elongate slot, through which a second pin passes with clearance, the pivoting movement of the blade being limited by interengagement of one or the other sides of the second hole with the second pin.

Preferably the tool includes guide means assisting the positioning of the tool with respect to a cable. Such guide means may comprise a projection from the tool body adjacent the opening and having graduations or other indexes for alignment with the cable end or an annular cut already formed therein.

In an alternative form of the tool, the cutting blade may be set relative to the body at a slight angle to a strict radial plane of a cable located in the opening, whereby rotation of the tool around the co-axial cable in the sense causing the blade to effect a shallow cut causes the body to be threaded along the cable, whilst at the same time severing the outer insulating layer. The severed outer layer thus is in the form of a helicoid, at the completion of the severing operation, and may with great facility be removed from the cable simply by pulling the free end portion of the helicoid in an axial direction. Rotation of the tool in the other sense around the cable, to sever all of the layers except the inner core, should not cause axial movement of the tool along the length of the cable, in view of the considerably great depth of penetration of the cutting blade.

The body of the tool may suitably be profiled to lend itself to the ready rotation thereof around a co-axial cable. For example, the body or the blade carrier (if provided) may include a rounded finger hole. In an alternative arrangement, the blade may be pivoted directly to the body and be appropriately profiled to permit the application of a force thereto to drive the blade-and hence the body-around the coaxial cable to be prepared. In such a case the same severing action can be obtained, because the body will tend to trail behind the rotation of the blade, owing to the friction between the body and the cable, so following the rotation of the blade in whichever sense a rotative force is given to the blade.

By way of example only, one specific embodiment of co-axial cable stripping tool constructed in accordance with this invention will now be described in detail, reference being made to the accompanying drawings, in which: Figure 1 is a front view of the tool; Figure 2 is a side view of the tool of Fig. 1 but with its cover plate separated from the main body and the elastic band partially cut away, for clarity; Figure 3 is a detailed part-view of the tool of Figs. 1 and 2, showing the cutting blade in a first position; and Figure 4 is a detailed view of the cutting blade, but in its second position.

Referring to the drawings, the cable stripping tool there shown has a body 10, assembled from three moulded plastics material parts comprising a main body 11, a cover plate 12 and a blade carrier 13. The main body 11 and cover plate 12 fit together to define a slot within which a portion of the blade carrier 13 may slide, as will be apparent from the following description.

The main body 11 has a side plate 14 from which a generally U-shaped wall 15 upstands, leaving a flange 16 projecting beyond the Ushaped wall. In association with the side plate 14, the inner faces of the wall 15 define the slot 17 within which a generally rectangular portion of the blade carrier 13 may slide. The moulding of the main body 11 may include recesses 18, to reduce the amount of plastics material employed and also to permit satisfactory production of the part by an injection moulding process, taking into account material shrinkage.

The cover plate 12 is of substantially the same overall shape as the side plate 14, and has a flange 19 arranged in a similar manner to the flange 16 of the main body 11. Five pins 20 project normally from the cover plate, which pins are received in bores 21 provided in the main body, to locate and hold the cover plate in the required position with respect to the main body 11. Pins 20 and bores 21 may appropriately be formed so that the main body and cover plate snap-fit together, or reliance may be placed simply on a frictional interfit between the pins and bores. Alternatively, the cover plate and main body may be glued together during the last stage of assembly of the tool.

A bore 22 is formed through the side plate 14, which bore is of an appropriate diameter closely to receive the co-axial cable with which the tool is intended to be used. The inside face 23 of the base of the U-shaped wall 15 extends substantially diametrically of the bore 22, and that wall is provided with a semi-circular groove 24 contiguous with the bore 22, so as to permit a cable to be in serted through the bore 22 to the required extent. The cover plate 12 similarly is formed with a bore 25 co-axial with and of the same diameter as the bore 22, and on the outer face of the cover plate adjacent the bore 25 there is provided a guide piece 26, having two guide surfaces 27 and 28, for a purpose to be described below.

The blade carrier 13 has a finger portion 29 including a finger hole 30 and a moulding re cess 31 in which may be provided for example information concerning the particular sizing of the tool. Projecting from the finger portion 29 is a blade portion 32, adapted for sliding movement within the slot 17 defined by the main body 11. The top face 33 of this portion 32 is provided with a semi-circular groove 34, centrally positioned for alignment with the bore 22 in the main body 11.

The blade portion 32 of the blade carrier 13 is provided with two pins 35 and 36 upstanding from that portion and having a cutting blade 37 pivotally mounted on pin 35. In addition to the hole adjacent the blade end remote from the cutting edge 38 closely fitting on the pin 35, the blade has a slot 39 in which is received pin 36. When so positioned, the cutting edge 38 of the blade is cordal with respect to the groove 34.

The blade 37 is of closely controlled dimensions and shape. The side edge of slot 39 is tangential to the hole for pin 35 and the cutting edge 38 is accurately honed to lie at a predetermined acute angle to the major axis of the slot 39, a known distance from the hole which receives the pin 35. In addition, the relative positions of the pins 35 and 36 with respect to the groove 34 of the carrier 13 are closely controlled.

It will thus be appreciated that with the blade pivoted to the position shown in Fig. 3, with the pin 36 engaging the right-hand edge of the slot 39, the amount by which the cutting edge 38 overlies the groove 34 can be controlled by appropriate positioning of the pin 35. When the blade has pivoted so that the left hand side of the slot 39 engages the pin 36 (as shown in Fig. 4) the amount by which the cutting edge 38 overlies the groove 34 is increased, but limited by the spacing between the pins 35 and 36. Thus, complete control of the two depths of cut, with the blade in the two positions shown in Figs. 3 and 4 respectively, can be achieved solely by appropriate positioning of the pins 35 and 36.

As shown in Fig. 2, the pins 35 and 36 project beyond the U-shaped wall 15 of the main body 11 to be received in a groove 40 in the cover plate 12. When the tool is completely assembled, this groove 40 limits the movement of the blade carrier 13 away from the main body 11.

The tool is completed by means of a resilient endless band 41 passed around the Ushaped wall 15, between the flanges 16 and 19, and around the finger portion 29 of the blade carrier 13. When so positioned, the band 41 should be in a state of tension, so that it holds the blade carrier 13 fully engaged in the slot in the main body 11. To facilitate relative separation of the blade carrier and the main body 11 to the extent limited by pin 35 in groove 40, finger and thumb friction grip portions 42 and 43 are provided respectively on the side plate 14 and cover plate 12.

The above described tool is especially confi gured for use with a particular co-axial cable, to give a specified form of end portion prepa ration. When a cable of the correct type is to be prepared, the tool is "opened" by pulling the blade carrier 13 away from the main body 11 against the resilient bias provided by the band 41, conveniently effected by inserting the middle finger through finger hole 30 and grasping the body between a thumb and forefinger, on grips 42 and 43. Holding the tool open, the operator then pushes the cable through bore 22, past grooves 24 and 34 and through bore 25 in plate 12. The tool is then released to permit the band to draw the blade carrier 13 into the main body, whereafter the tool is rotated in a clockwise sense (as viewed in Fig. 1) with the cable end-on.The drag of the blade on severing the layers of the cable causes the blade to move to the position illustrated in Fig. 4 and so the blade effects a relatively deep cut, partially severing the insulating first layer overlying the core of the cable.

The tool is then opened again, and the cable pushed further through the bore until the cut already effected is aligned with guide surface 27 of the guide piece. Then, the projecting portion of the cable is twisted, until little resistance is felt, so indicating that the end portion of the insulating first layer of the cable has been completely severed. This action also will twist together the strands of a multistrand core conductor. The' tool is then rotated clockwise again, so effecting a second cut partially severing the insulating first layer of the cable, the blade acting in precisely the same manner as has been described above.

Preferably, the tool is at this point rotated counterclockwise, to move the blade to the position illustrated in Fig. 3, to prevent the blade cutting right through the insulating third layer in the initial part of the next stage, described below.

In the next stage of the operation, the tool is opened again and the cable pushed yet further through the bore in the tool, until the first cut is aligned with the second guide surface 28 of the guide surface 26. It is then rotated in a counterclockwise direction and this time the blade pivots automatically to the position illustrated in Fig. 3, so performing a relatively shallow depth of cut, severing on the outer insulating third layer of the cable and leaving untouched the conducting second layer and the insulating first layer. To complete the preparation, the tool is gripped across its ends, so urging the recesses 24 and 34 on to the severed part of the cable, and the tool is then pulled towards the free end of the cable, the blade still being engaged in the third cut.This pulls all of the severed layers clear of the cable, so leaving exposed a portion of the inner conductor, a length of the insulating first layer and a length of the conducting second layer.

When using the tool of this invention, it will be appreciated that the blade need not immediately penetrate the cable to the required depth. The severing action may be gradual, as the tool is rotated, with the band 41 gradually drawing the blade into the cable to the predetermined depth, as tool rotation is continued. Moreover, the operation of the tool is fully automatic in that the blade moves to either one of its two positions by virtue of the drag of the blade through the cable, depending on whether the tool is rotated clockwise or counterclockwise.

Modification of the tool to suit different cables is relatively simple. Identical mouldings may be used, with the bores 22 and 25, and the grooves 24 and 34 appropriately machined to suit the cable with which the tool is to be used. Moreover, the holes in the carrier to receive the pins 35 and 36 may be jigdrilled at appropriate positions to give the required two depths of cut for any given cable.

The tool also may be modified to have the blade carrier removable from the body, by appropriate configuration of pins 35 and 36, and of the plate 12 in the region of slot 40. This will faciiitate the changing of a blade, when blunted by repeated use. Spare blades may be carried in an appropriate recess, formed in the blade carrier for instance on the opposite face thereof to that from which pins 35 and 36 project.

In a further alternative, the blade carrier 13 may include a slidable jaw opposed to and spring-urged towards recess 24 in the body.

This jaw will engage the cable immediately on releasing the blade carrier, even though the blade may not have penetrated the cable so preventing the recess 34 engaging the cable.

Such a jaw will serve to clamp the cable against recess 24, and also to hold the tool square, until the blade has sufficiently penetrated the cable on rotating the tool.

Claims (14)

1. A tool suitable for stripping distinct layers from a multi-layer elongate member, which tool comprises a body defining an opening in which may be received the member to be stripped, and a cutting blade pivotally mounted with respect to the body and movable between the two limiting positions in the first of which the cutting edge of the blade projects to a relatively large extent into the opening and in the second of which the cutting edge projects to a relatively lesser extent into the opening, whereby following the location of a multi-layer member in the opening and rotating the tool around the member in one sense, the blade is caused to move to one limiting position such that the cutting edge substantially severs several layers of the member, but on rotating the tool around the member in the other sense the cutting blade is caused automatically to move to its other limiting position such that the cutting edge severs fewer layers of the member.

2. A tool according to claim 1, wherein the cutting blade is pivotally mounted on a carrier which carrier is slidably mounted with respect to the body, whereby the blade may be moved clear of the opening by sliding movement of the carrier.

3. A tool according to claim 2, wherein a resilient bias is provided between the carrier and body, to urge the blade towards the opening.

4. A tool according to any of the preceding claims, wherein the opening is in the form of a through-bore, in which the cable may be received.

5. A tool according to any of the preceding claims, wherein the blade has a mounting hole by means of which the blade is pivoted to a pin provided on the tool body or carrier, if provided.

6. A tool according to claim 5, wherein the blade has a second hole though which a second pin passes with clearance, the pivoting movement of the blade about the first-mentioned pin being limited by interengagement of the side of the second hole with the second pin.

7. A tool according to claim 6, wherein the second hole is n the form of an elongate slot.

8. A tool according to any of the preceding claims and further comprising guide means adapted to assist the positioning of the tool with respect to a member, when a cut is to be made in the member.

9. A tool according to claim 8, wherein the guide means comprises a projection from the tool body adjacent the opening therein and having graduations or other indexes for alignment with the member end or a cut already formed therein.

10. A tool according to claim 1, wherein the cutting blade is set relative to the axis of the opening in the body at a slight angle to a strict radial plane of the opening, whereby rotation of the tool around an elongate member may cause the body to be threaded along the member.

11. A tool according to claim 10, wherein the body of the tool is profiled to lend itself to the ready rotation thereof around an elongate member.

12. A tool according to claim 1, wherein the blade is pivoted directly to the body and is appropriately profiled to permit the application of a force thereto to drive the blade around the elongate member to be prepared.

13. A tool according to claim 1 and substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.

CLAIMS Amendments to the claims have been filed, and have the following effect: Claims 1 to 13 above have been deleted or textually amended.

New or textually amended claims have been filed as follows:- 1. A method of preparing the end portion of a co-axial cable using a tool having a bore for receiving the cable which bore extends through the tool from a face thereof, the tool further having a cutting blade arranged to cut into a cable located within the bore, and having a guide piece upstanding from said face of the tool, which method includes the steps of: retracting the cutting blade from the bore; passing the cable through the bore to project from said face of the tool; moving the cutting blade to a cable-cutting position and effecting a first annular cut into the cable by rotating the tool around the cable; retracting the cutting blade from the bore; advancing the cable further through the bore until the first annular cut is aligned with a graduation or other index of the guide piece; and moving the cutting blade to a cable-cutting position and effecting a second annular cut into the cable by rotating the tool around the cable.

2. A method according to claim 1, in which a third annular cut is effected around the cable following completion of said first and second annular cuts, by the steps of: retracting the cutting blade from the bore; advancing the cable yet further through the bore until the second annular cut is aligned with a graduation or other index of the guide piece; and moving the cutting blade to a cable cutting position and effecting a third annular cut into the cable by rotating the tool around the cable.

3. A method according to claim 2, in which the first and second annular cuts are aligned with different graduations or other indexes of the guide piece, in each case prior to effecting the respective second and third annular cut.

4. A method according to claim 2, in which the first and second annular cuts are aligned with the same graduation or other index of the guide piece, in each case prior to effecting the respective second and third annular cut.

5. A method according to any of the preceding claims, in which the cable is advanced further through the bore following completion of an annular cut until that annular cut is aligned with a guide surface of the guide piece.

6. A method according to claim 1, in which the first annular cut is effected to a relatively great depth, the second annular cut is effected to a relatively shallow depth.

7. A method according to any of claims 2 to 5, in which the first and second annular cuts are effected to relatively great depths, whereas the third annular cut is effected to a relatively shallow depth.

8. A method according to claim 7, in which the first and second annular cuts are effected to substantially The, same depth.

9. A method according to claim 7, in which the end portion of the cable is rotated about the cable axis and with respect to the remainder of the cable following completion of the first annular cut but prior to effecting the second annular cut.

10. A method according to any of the preceding claims, in which the cable end preparation is completed following the last cable-cutting operation by pulling the tool axially of the cable towards the cable end whilst maintaining the cutting blade in its cable-cutting position, thereby stripping the severed portions from the main length of the cable.

11. A method of preparing the end portion of a co-axial cable according to claim 1 and substantially as hereinbefore described, with reference to the accompanying drawings.

12. A tool for preparing the end portion of a co-axial cable, which tool comprises a body defining a bore in which may be received the cable to be prepared, a cutting blade mounted on a carrier itself mounted on the body for movement with respect to the body so that the cutting blade may be moved towards and away from the bore whereby a cable located within the bore may be cut by the blade upon rotation of the tool around the cable, a resilient bias acting between the tool body and the carrier to urge the blade towards a cable-cutting position, and guide means adapted to assist the positioning of a cable within the bore prior to a cut being made into the cable, the guide means comprising a projection from the tool body adjacent the bore therein and having graduations or other indexes for alignment with the cable end or an annular cut already formed in the cable.

13. A tool according to claim 12, wherein the projection is of arcuate cross-sectional shape centred on the bore and has an end face located in a radial plane which end face may be used for alignment with an annular cut already formed in the cable.

14. A tool according to claim 13, wherein the projection has a further end face also located in a radial plane which further end face is positioned between the tool body and the first-mentioned end face.