GB2288695A - Cable stripper - Google Patents

Abstract

A cable stripper which is particularly suitable for stripping mineral insulated cable, has a stripping assembly (3 Figures 1 and 3) comprising jaws 40, 42 whose separation can be varied in order to locate a cable between them, an adjustment ring 44 (Figure 5) for varying the separation of the jaws and a cutter blade 66 mounted on at least one of the jaws. The jaws 40, 42 are arranged around the axis of the ring 44 so that a cable located by the jaws will be substantially coaxial with the ring, and the ring has a camming surface for each jaw so that rotation of the ring will move the jaws radially. The ring 44 has indentations to give discrete separations of the jaws corresponding to different sizes of cable, indicia (72) on the ring 44 being provided to help the choice of separation. The stripper has a motor (2 Figure 2) for rotating the assembly about the axis so that the blade will cut the cable around its circumference. A braking mechanism (80 Figures 6 and 7) may be provided to clamp the cable and allow the stripped sheath to fall off. <IMAGE>

Description

CABLE STRIPPER This invention relates to devices for stripping electric cables, especially although not exclusively, for stripping mineral insulated cables, that is to say cables of the kind comprising at least one conductor insulated from a surrounding metal sheath, and where there is more than one conductor from the other conductor or conductors, by compacted mineral insulating powder, usually but not necessarily magnesium oxide.

In order to terminate such cables it is necessary to cut back the metal sheath a predetermined distance to expose the central conductor or conductors which can be relatively difficult due to the mechanical toughness of the cables as compared with other cables. It is an object of the present invention to provide a device preferably a mains powered device, which is simple to use and can strip cables of a range of diameters.

According to the present invention, there is provided a cable stripper having a stripping assembly which comprises: (i) a plurality ofjaws whose separation can be varied in order to locate a cable between them; (ii) an adjustment ring for varying the separation of the jaws; and (iii) a cutter blade mounted on at least one of the jaws; the jaws being arranged around the axis of the adjustment ring so that a cable located by the jaws will be substantially coaxial with the ring, and the ring having a camming surface for each jaw so that rotation of the ring about its axis will move the jaws radially toward or away from its axis, the stripper including means for rotating the assembly about the said axis so that the blade will cut the cable around its circumference.

In order to strip a length of cable employing the stripper according to the invention, the adjustment ring is rotated to bring the jaws to the appropriate separation for that cable and the end of the cable is inserted between the jaws until it abuts the blade. Alternatively, the jaws may be opened, the cable inserted and then the jaws closed about the cable by rotation of the adjustment ring. Whichever order is employed the jaws should not grip the cable but should be slidable over the cable while locating it in its correct position. The stripping head assembly is then caused to rotate about the cable thereby causing the blade to cut the cable sheath circumferentially. The blade is preferably oriented at an acute angle to the axis ofthe ring (and cable) and/or is appropriately shaped so that it will cut the cable helically around its circumference, drawing more cable axially toward the blade as the assembly rotates. The assembly can simply be caused to rotate, for example by supplying power to a mains operated electric motor in the stripper, until an appropriate length of sheath has been removed. Preferably the adjustment ring and jaws are so arranged that the jaws can be moved toward the axis of the ring with substantially no movement ofthejaws along the axis. Such an arrangement will reduce the possibility that the blade will move axially away from the end of the cable as the jaws are closed, thereby preventing the blade biting into the cable and pulling more cable toward it as the head assembly is manually rotated.

The assembly may be provided with any number ofjaws, although the more jaws provided the more complicated the assembly becomes. In practice a pair ofjaws is sufficient although in such a case it is preferred for at least one, and especially both, jaws to have an indentation in line with the axis of the ring in order to ensure correct positioning of the cable.

The camming surfaces on the ring may have any of a number of designs.

For example they may be directed radially inwardly and bear on the jaws to cause them to close, in which case the jaws may be biassed radially outwardly, i.e. to open. Alternatively the camming surfaces may be directed radially outwardly and bear on the jaws to cause them to open, in which case the jaws may be biassed to close. It is also possible for a pair of oppositely directed camming surfaces to be arranged in the form of a slot that encloses a pin on the jaws, thereby obviating the need for any biassing spring to act on the jaws.

Each camming surface may, if desired, extend over only a sector of the adjustment ring so that, for example, rotation of the ring through 360/n degrees (where n is the number ofjaws) will move the jaws between their fully open and fully closed positions. Preferably, however, each calming surface extends circumferentially around substantially the entire adjustment ring so that rotation of the ring through one revolution will cause the jaws to move between their fully open and fully closed positions. In such a case the camming surfaces for different jaws will need to be offset from one another along the axis of the adjustment ring.

The assembly may be arranged so that the adjustment ring, and hence the jaw separation, may be altered continuously between the maximum and minimum jaw separation. However, it is preferred for the assembly to include a stepping arrangement that retains the jaws preferentially at a number of discrete separation positions. This stepping arrangement may, for example, co-operate with the adjustment ring and restrict it preferentially to a number of discrete positions on a support member which forms part of the assembly.

Advantageously the assembly includes a brake or other means that can be applied to the cable, preferably at will, in order to prevent more cable being drawn toward the balde as the assembly rotates. Application of such a brake or other means will cause the blade to cease cutting the cable helically and instead form a circular cut, thereby allowing the stripped length of cable sheath to be removed from the cable.

Any means conventionally employed for rotating the cutting blade of a cable stripper may be employed in the stripper according to the invention, but preferably a means powered electric motor is used.

One form of cable stripper according to the present invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a side view of the cable stripper; Figure 2 is a sectional elevation of the stripper taken from the other side; Figure 3 is a sectional elevation of the stripper taken along the axis of the cable to be stripped; Figure 4 is a sectional elevation of the cable stripping assembly of the stripper on a larger scale along the axis of the cable to be stripped, and Figure 5 is a side view of the assembly of figure 4, and Figures 6 & 7 are side views of an alternative form of stripper.

Referring to the accompanying drawings, a cable stripper comprises a moulded plastics housing 1, a 500W, 1 10V single phase electric motor 2 and a cable stripping assembly 3. The housing 1 is formed in conventional manner in two halves 4 and 6 and includes a pistol-grip 8 that houses a trigger 10, electrical switch 12 actuated by the trigger, and an inlet for a power cable 14 for supplying power to the motor. The motor shaft 16 is supported by forward and rear bearings 18 and 20 and transmits power to the stripping assembly 3 via a drive shaft 22 supported by forward and rear bearings 24 and 26, gears 28 and 30 between the motor shaft 16 and drive shaft 22, worm gear 32 on the drive shaft and a gear 34 on the stripping assembly.

The stripping assembly 3 comprises a hollow shaft 36 that extends laterally through the housing 1 and can accommodate a mineral insulated cable (not shown) of any diameter within a predetermined range. The shaft 36 ends in the form of a disc-shaped support member 38 on the external surface of the housing 1. A pair ofjaws 40 and 42 are located on the support member 38 and are disposed on opposite sides ofthe axis ofthe shaft, and an adjustment ring 44 is also located on the support member coaxially with the shaft 36 and encloses the jaws 40 and 42 within it.

Each jaw 40 and 42 has a pin 46 and 48 that is located in a corresponding recess in the support member 38 and is acted on by a spring 50 and 52 to bias the jaw radially outwardly from the axis of the shaft 36 against the internal surface of the adjustment ring. The internal surface of the adjustment ring has a pair of camming surfaces 54 and 56, that are located adjacent to one another along the axis ofthe shaft 36. Each camming surface 54 and 56 bears on a corresponding bearing surface 58 and 60 ofthejaws 40 and 42 so that rotation ofthe adjustment ring 44 will cause the jaws 40 and 42 to open or close symmetrically about the axis of the shaft 36. A region 62 ofjaw 40 that is located adjacent to the bearing surface 58 is cut back in order to prevent it bearing on the raised parts of the camming surface 56 of the adjustment ring.

Similarly a region 64 ofjaw 42 adjacent to the bearing surface 60 is cut back to prevent it bearing on the raised parts of camming surface 54.

Jaw 42 is provided with a cutting blade 66 which may be replaced and which, when fitted on the jaw will protrude from the surface of the jaw by about 0.5 to 1.5mm in order to cut the metal sheath of the cable.

The support member 38 has a recess in which a spring 68 is located that biasses a small metal ball 70 against the rear surface of the adjustment ring 44.

The rear surface of the adjustment ring has a circular array of indentations (not shown) centred around the axis of the shaft 36 which co-operates with the ball 70 and cause the adjustment ring to remain preferentially at a number of discrete orientations with respect to the support member corresponding to the location of the indentations, thereby restricting the jaw separation to discrete multiples of 0.1 mum. Identification codes 72 and/or jaw separation data may be provided on the adjustment ring to assist operation.

In use, if the size of cable to be stripped is known, the jaw separation may be adjusted by aligning the appropriate code 72 with arrow 74 on the assembly and the end of the cable is then inserted into the shaft 36 until its end is located between the jaws 40 and 42 and abuts the blade 66. Alternatively, the jaws may be opened by twisting the adjustment ring, the cable inserted into the shaft 36 and thejaws closed about the cable until they grip it. Opening the jaws by one position of the adjustment ring 44 will ensure that the jaws may rotate about the cable. The motor 2 is then actuated by means of the trigger 10, causing the shaft 36 and the stripping assembly 3 to rotate. The cutting blade is so shaped that it bites into the cable cutting it helically around its circumference and causing more cable to be drawn into the shaft 36. This is continued until a sufficient length of cable has been stripped, and the stripped length of cable sheath can then be cut off using a pair of snips.

A modification of the stripper is shown in figures 6 and 7. This stripper operates in the same way as that described in figures 1 to 5, with the exception that a brake mechanism 80 is provided. The brake mechanism is mounted on the left side of the stripping assembly and comprises a pair of braking arms 82 and 84 that are connected by pin 86 at one end thereof and are biassed to an open position. The brake can be operated by squeezing the other ends 88 and 90 of the arms 82 and 84 together causing the arms to clamp the cable. This prevents more cable being drawn toward the cutting blade and causes the blade to revolve around the cable in a circular path, thereby allowing the stripped length of cable sheath (swarf) to fall off or be removed.

Claims (9)

1. A cable stripper having a stripping assembly which comprises: (i) a plurality ofjaws whose separation can be varied in order to locate a cable between them; (ii) an adjustment ring for varying the separation ofthejaws; and (iii) a cutter blade mounted on at least one of the jaws; the jaws being arranged around the axis of the adjustment ring so that a cable located by the jaws will be substantially coaxial with the ring, and the ring having a camming surface for each jaw so that rotation of the ring about its axis will move the jaws radially toward or away from its axis, the stripper including means for rotating the assembly about the said axis so that the blade will cut the cable around its circumference.

2. A stripper as claimed in claim 1, wherein the adjustment ring and jaws are arranged so that the jaws can be moved toward the axis of the ring with substantially no movement along the axis.

3. A stripper as claimed in claim 1 or claim 2, wherein the blade is oriented at an acute angle to the axis of the ring so that it will cut the cable helically around its circumference.

4. A stripper as claimed in any one of claims 1 to 3, in which a pair ofjaws are provided.

5. A stripper as claimed in any one of claims 1 to 4, wherein the camming surfaces on the ring are directed radially inwardly to cause the jaws to close, and the jaws are biassed radially outwardly.

6. A stripper as claimed in any one of claims 1 to 5, wherein the camming surface for each jaw extends circumferentially around substantially the entire adjustment ring so that rotation of the ring through one revolution will cause the jaws to move between fully open and fully closed positions.

7. A stripper as claimed in any one of claims 1 to 6, which includes a stepping arrangement that retains the jaws preferentially at a number of discrete separation positions.

8. A stripper as claimed in claim 7, wherein the stepping arrangement restricts the adjustment ring preferentially to a number of discrete positions on a support member.

9. A cable stripper substantially as hereinbefore described with respect to, and as shown in the accompanying drawings.