GB2069246A - A tool for cutting a taper on an electric cable insulation - Google Patents

Abstract

A tool for cutting a taper in the insulating layer 12 of an electric cable comprises a clamp 16, for clamping securely about a bared portion of the cable conductor 10 and an assembly journalled about the clamp 16 and carrying a cutting blade 30. Manual rotation of said assembly about the clamp 16 drives the cutting blade to effect a helical cut in the insulating layer 12 to cut the required taper. Because the cutting blade is guided relative to the conductor 10, and the conductor is reliably circular, then a reliably concentric taper will be cut. <IMAGE>

Description

SPECIFICATION A tool for cutting a taper on an electric cable insulation This invention relates to a tool for cutting a taper in the insulating layer of an electric cable.

When jointing electric power cables it is necessary to cut a taper in the insulating layers of the cables. In hitherto used tools, the outer circumference of the insulation is relied upon to guide the cutting blade.

In the case of cables having elastomeric insulation, particularly large diameter cables, the insulation is not perfectly circular, nor is it exactly concentric about the conductor. Therefore these tools do not provide a good concentric taper (or chamfer) on the insulation.

In accordance with this invention, there is provided a tool for cutting a taper in the insulating layer of an electric cable, comprising a cutting blade and means for guiding the cutting blade relative to a circular conductor core of the cable as the cutting blade cuts a taper in the cable insulation.

Although the invention has particular application to cables with elastomeric insulation, it may also be used on cables having paper insulation.

In an embodiment to be described herein, the tool comprises a clamp portion which clamps about the circular conductor core, once a length of this core has been bared of the overlying insulation. The cutting blade is guided relative to this clamping portion.

An embodiment of this invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is an end view of a cutting tool in accordance with the invention when applied to a cable the insulation of which it is to cut; and Figure 2 is a section on the line A-A of Figure 1.

Referring to the drawings, a cutting tool in accordance with this invention is shown applied to the end of an electric power cable the core of which comprises a single conductor 10 of circular cross-section.

The cable shown comprises an elastomeric insulation 12 applied over a tubular inner screen 14. The tool may instead be applied to a cable having multi-conductor core and/or a paper insulation.

The tool comprises a diametrically split clamp 16 arranged to be clamped securely about the conductor core after a length of say 60 mm of the insulation has been stripped from the end of the core, as shown. A ring 18 is rotatably mounted on the clamp 16 by means of a ball race bearing assembly 20. The ring 18 and ball race assembly 20 are not shown in Figure 1. The tool further comprises a support ring 22, spaced from ring 18 and secured thereto by arms 23 and 24, so that the two rings are co-axial. A nylon bush 26 is fitted onto the cable, with its inner diameter dimensioned so as to embrace the insulation, and its outer diameter dimensioned so the ring 22 embraces the bush 26. The assembly of rings 18, 22 and arms 23, 24 is thus rotatable about the cable axis by ring 18 being journalled to the clamp 16 through bearing assembly 20 and ring 22 being rotatably supported on bush 26.

A ring 28 carrying a cutting blade 30 and a guide blade 32 is disposed between the rings 18 and 22 and is mounted on the arms 23,24 for sliding axially of these rings, whilst being rotatable with the assembly of rings 18,22 and arms 23,24. Thus, arms 23 and 24 pass through slots provided in ring 28.

Cutting blade 30 and guide blade 32 are positioned on diametrically opposite sides of the ring 28 and are each mounted to the ring 28 so as to lie in a transverse plane, to which the common axes of rings 18,22 and 28 are perpendicular, and to be slidable radially.

In particular, the cutting blade is elongate and has a cutting edge 30a on one of its long edges, extending radially of the common axes of the three rings, being provided by a chamfer on that major surface of the cutting blade which faces the split clamp 16. The cutting blade also has a cutting edge 30b formed by a chamfer at one end edge of a short wall extending from the radially inner end of the cutting blade towards clamp 16, said wall being perpendicular to the main portion of the cutting blade. The chamfer forming cutting edge 30b is on the radially outer major surface of said wall and is adjacent cutting edge 30a.

The guide blade 32 has an edge 32a aligned with cutting edge 30a and a radially inner edge 32b parallel to cutting edge 30b. Although guide blade 32 is set in the same transverse plane as cutting blade 30, it is provided at its inner end with opposite relieved guide surfaces 34,35 for a purpose to be described later in this specification.

The guide blade is urged radially inwards by a tension spring 36 and a screw 38 is adjustable to limit the radially inwards travel of the guide blade.

The cutting blade is adjustably set by means of a screw 40, passing through a longitudinal slot 42 in the cutting blade, clamping the cutting blade to a peg 44 which isslidably received in a slot 46 in a taper guide arm 48. This taper guide arm is pivoted at 50 to arm 24 and a clamp 52 is provided at its other end whereby it may be clamped at any desired point along a graduated radius arm 54 projecting from support ring 22.

In use, a length of say 60 mm of the insulation is stripped from the end of the cable as shown. A bush 26, selected of appropriate size for the cable concerned, is applied over the insulation and the tool is then applied to the cable and the split clamp 16 (also of selected appropriate size) secured about the bared conductor, with the support ring 22 embracing the bush 26.

The taper guide arm 48 is clamped to the radius arm 54to provide the required angle oftaperto be cut. The ring 28, carrying the cutting blade, is positioned at the cut end of the insulation and the radial position of the cutting blade is adjusted to the outer diameter of the screen 14. The guide blade is similarly adjusted.

The assembly comprising rings 18,22 and 28 and arms 23,24,54 is then manually rotated, in the direction indicated by the arrow shown in Figure 1, using bars 56 projecting radially from ring 28, whilst at the same time applying pressure to these bars to urge ring 28 away from ring 18 and towards support ring 22. The cutting blade accordingly proceeds to cut helically around the insulation, the pitch of cut being determined by the spacing of guide face 35 from the front plane of the cutting blade, this guide face being urged against the flat end of the insulation as a result of the axial pressure applied to bars 56.As the cutting proceeds, and ring 28 slides axially along the cable, the cutting blade is guided radially outwards by engagement of the peg 44 in the slot of taper guide arm 48, until eventually the cutting blade reaches the outer diameter of the insulation, at which point the cutting of the taper is complete and the tool can be removed. Throughout cutting, the end edge 32b of the guide blade follows a portion of the tapered surface which has just been cut, and accordingly the guide blade is progressively displaced radially outwards. However, at any instant the flat guide surface 35 is maintained in contact with an annular transverse end surface of the insulation, which is radially outwards of the tapered surface at that time, and which is about to be cut by the cutting blade. The ring 28 and guide and cutting blades are shown dotted in the final position.

The guide blade may be removed, turned over and replaced so that the surface 34 faces the cable insulation. The surfaces 34,35 are at different spacings from their adjacent major surfaces of the guide blade so as to determine different values of the pitch for the helical cut made by the cutting blade, depending which way round the guide blade is assembled.

The tool which is shown in the drawings is intended to cover a range of cable sizes, with the core diameter in the range 25 to 30 mm and insulation diameter in the range 50 to 80 mm.

The taper cut by the tool is found to be superior to that cut by prior art tools in that it is concentric about the circular core and can commence on the outer surface of the screen 14 whilst leaving this screen intact.

The tool may be modified by making the three rings and bush 26 of split construction, so that the tool may be opened and then closed around a cable, instead of being slid over the end of the cable. Then a taper may be cut in the insulation at any desired position along its length.

Claims (1)

1. Atool for cutting a taper in the insulating layer of an electric cable, comprising a cutting blade and means for guiding the cutting blade relative to a circular conductor core of the cable as the cutting blade cuts a taper in the cable insulation.

2. A tool as claimed in claim 1, in which the guiding means is arranged such that the cutting blade executes a helical cut of progressively changing radius in said insulating layer.

3. Atool as claimed in claim 1, in which the guiding means comprises a clamping portion for clamping about a bared portion of said circular conductor core, the cutting blade being guided relative to said clamping portion.

4. A tool as claimed in claim 3, in which the cutting blade is mounted for rotation relative to said clamping portion, said guiding means including means for regulating the radial position of the cutting blade according to its position along the cable from the clamping portion.

5. A tool as claimed in claim 4, in which the guiding means comprises a guide blade arranged to rotate with rotation of the cutting blade and determining the pitch of the helical cut.

6. A tool as claimed in claim 5, arranged for the helical cut to proceed from the bared portion of the conductor core and thus form the taper from its narrower end to its wider end, the guide blade being urged against the transverse end surface of the insulation radially outwards of the tapering surface being formed, and the guide blade also being urged radially inwards against the tapering surface being formed.

7. A tool as claimed in claim 6, in which the guiding means comprises a bush for fitting over the cable insulation and rotatably supporting one end of an assembly which carries the cutting and guide blades, said blades being slidable together lengthwise of said assembly and the other end of said assembly being rotatably supported on said clamping portion.

8. A tool as claimed in claim 7, in which said regulating means comprises a guide arm carried by said assembly and extending generally lengthwise of said assembly with the cutting blade slidably engaged with said guide arm, the guide arm being adjustably pivotable to a selected position to predetermine the angle of taper which is cut in the cable insulating layer.

9. A tool as claimed in any preceding claim, arranged so that it may be closed around a cable at any selected position along its length and remote from its ends, at which position a length of the cable insulating layer has been removed,.for the purpose of cutting a said taper in the insulating layer at that position.

10. Atool substantially as herein described with reference to the accompanying drawings.

11. An electric cable having an insulating layer with a taper cut therein by a tool as claimed in any preceding claim.

New claims or amendments to claims filed on 19th May 1981.

Superseded claims 1 and 3 New or amended claims:- Original claims 4 to 11 renumbered as 3 to 10 respectively and appendancies corrected.

1. A tool for cutting a taper in the insulating layer of an electric cable, comprising a cutting blade and means for guiding the cutting blade relative to a circular conductor core of the cable as the cutting blade cuts a taper in the cable insulation, the guiding means comprising a clamping portion for clamping about a bared portion of said circular conductor core, the cutting blade being guided relative to said clamping portion.