GB2438902A

GB2438902A - Knife for stripping outer sheath of cable with varying depth of cut.

Info

Publication number: GB2438902A
Application number: GB0611504A
Authority: GB
Inventors: John James Pimley
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-06-10
Filing date: 2006-06-10
Publication date: 2007-12-12
Also published as: GB0611504D0

Abstract

A knife has a detachable blade 15 mounted at one end of a blade carrier 18, the other end of the blade carrier 18 is connected, via a flexible strip 8, to the main body of the knife 5. A hand operated screw 9 with a tapered end is able to move the blade carrier 18 and hence the blade 15 about a point 13 in a slightly curved path to allow the knife to cut different depths.

Description

Knife for stripping the outer sheath of electrical cables Electrical

cables connecting to electrical devices need to have a length of the outer sheath of the cable I removed to access the inner insulated wires. This is carried out by cutting the outer sheath circumferentially 2, then pushing or pulling the outer sheath off the wires, or, in the case of larger cables, also cutting the length of sheath to be removed in a longitudinal direction 3 such that it can be peeled off.

Although many devices have been patented, in practise, the.er)sheaths are mainly removed using a standard knife, an example being the Stanenife. This type of knife has an exposed blade with no depth-of-cut restrictions and frequently cuts through the outer sheath and into the insulation surrounding the inner wires.

This penetration of the wire insulation gives rise to potentially lethal problems if the live or neutral wires are exposed through the insulation.

The invention allows the adjustment of the depth of the exposed cutting edge of blade such that when the blade used for the circumferential cut 2 it does not penetrate the inner wire insulation. But, most importantly, because of the geometly of the invention the same adjustment gives the point of the blade lithe exact same depth of exposure as the main cutting edge 10; so that when the point of the blade is used for the longitudinal cut 3, the point does not penetrate the inner wire insulation.

To ensure that the inner insulation of a cable is not damaged, nor too much of the outer sheath is left intact after cutting, which would prevent effective stripping of the outer sheath, it is necessary that the exposed depth of the full length of the cutting blade and the exposed point is accurate to approximately 0.1mm. The cutting blade needs to have fine and accurate adjustment and also needs to be stable and not move under the cutting action.

Existing patented designs of cable sheath strippers, with adjustable blade-cutting depth, have limited market appeal as they have at least one of the following restrictions.

1 They can only cut circular cable and not flat cable.

2 They are also restricted in that they can only cut in the circumferential direction and not in the important longitudinal direction.

3 They are only suitable for one size of cable.

4 They need two separate adjustments of the blade, one for the circumferential cut and one for the longitudinal cut.

The design involves slides or gear wheel adjustment mechanisms that cannot give the required accuracy or stability unless supplemented by additional locking screws.

The invention can successfully cut the outer sheath of both round and flat cables in the circumferential direction and also cut the outer sheath of both round and flat cables in the longitudinal direction. The geometry of the design gives equal movement to the blade cutting edge and the cutting point from one adjustment screw.

The design has inbuilt accuracy and stability.

Details of the invention are contained in the accompanying drawings.

FIGURE I shows a typical round cable before and after the outer sheath has been removed. It also indicates the circumferential cut 2, the longitudinal cut 3 and the cut test-area 4.

FIGURE 2 shows the outside elevation of the knife.

FIGURE 3 shows a cross section of the knife in side elevation. This shows the blade 15, the blade-carrier 18, the flexible strip 8, which connects the blade-carrier 18 to the main body 5, and the spring 17. Also shown is the radius 23 between the point of flexure 13 of the flexible strip 8 and the point of the blade 11. Also shown is the radius 7 between the mid-point of the blade edge and the point of flexure 13 of the flexible strip 8. Also shown is the cutting face 14 which rests on the cable when canying-out the longitudinal cut 3.

FIGURE 4 shows in more detail the point of the blade 1 1. It shows the ideal path 21 that the blade point 11 should follow during the blade depth adjustment to ensure that the maximum cutting depth 20 of the blade point 11 and that of the main blade 10 are identical.

FIGURE 5 shows the true path of the blade during depth adjustment, this being an arced path of radius 23 from the point of flexure 13. It also shows the variation 22 of the arced path of the blade point from the ideal path 21.

FIGURE 6 shows the position of the knife relative to the cable 1, when using the cutting face 14 and blade point 11 to carry out the longitudinal cut 3, Fig 1. Cables of different manufacture and different size have different thicknesses of outer sheath. It is a fact that all cables to be fixed to an electrical device will need a length of exposed wire 4 where both the outer sheath and inner insulation will be removed.

As the length 4 of the inner wire insulation has to be removed to expose the wires for attachment to electrical equipment, it is of no consequence if the sheath-stripping knife penetrates the inner wire insulation in this area. Therefore this length of cable 4 will be used as a test area to determine the correct depth to which the exposed blade of the knife will be set. This will be on visual test-and-see basis until experience is gained.

Fig 2 & 3. The invention uses a detachable bladel5 mounted at one end of a blade-carrier 18. At the other end of the blade-carrier 18 is a flexible strip 8 which can be an integral part of the blade-carrier 18 or, as shown in the sketch, a separate flexible strip that has one end fixed to the blade-carrier 18.The other end of the flexible strip, whether it is integral with the blade-carrier 18 or a separate strip, is attached to the main body of the knife 5.

The blade-carrier 18 moves around the point of flexure 13, which is a point on the flexible strip between where the flexible strip is fixed to the body 5 and where the flexible strip is attached to the blade-carrier 18. The flexing of the strip allows the blade-carrier 18 to have a radial movement relative to the body 5.

It is essential that variations in the cutting depth of the exposed blade over its full length 6 be kept to a minimum in order to prevent penetration of the inner wire's insulation when cutting wide flat cable sheaths. This is ensured by having the ratio of the length of exposed blade 6 and the radius 7 from the point of flexure to the centre of the exposed part of blade 15 greater than 1:4 A hand operated screw with a taper on one end and a knurled head at the other end 9 moves the blade-carrier 18 and hence the blade 15 around the point of flexure 13 by using the tapered part 16 of the screw 9 to push down on the end of the blade-carrier 18.

When the screw is screwed in the direction toward the blade-carrier 18 the blade moves towards and through the opening 12 in the main body and increases the depth of the exposed blade 10. When the screw 9 is screwed in a direction away from the blade-carrier 18 the spring 17 or the natural elasticity of the flexible strip 8 causes the blade- carrier 18 and hence the bladel5 to move back into the into the main body and reduce the depth of the exposed blade 10.

Fig 4 & 5. The ideal path of the blade 21 has an angle a to a normal line at 9 0 to the main blade edge. This angle is determined by the geometry of the blade-carrier and its distance from the point of flexure 13. The cutting face 14 is angled at from the ideal path 21 according to the equation 3 = (90 -a).

The position of the point of flexure 13 and the dimensions of blade-carrier 18, allows the point of the blade 11 to move in a radial path that closely follows the ideal path 21.

The use of a screw 9 with a tapered end 16 to move the blade-carrier 18 allows fine adjustment of the depth of exposed blade 10.

The length of radius 23 and the position of the point of flexure 13 relative to blade 15 ensure that the radial path of the blade point 11, during blade depth adjustment, describes an arc that cuts the ideal path 21 at the minimum and maximum points of exposure of blade point beyond the cutting face 14. The line between these two points forms a chord of the arc and coincides with the ideal path 21.

Due to the length of the radius 23 and the position of the point of flexure 13 the maximum variation 22 of the arc from the ideal path is insignificant compared to the cutting depth 20 of the point 11, therefore the cable sheath can be pierced and cut in the longitudinal direction using the point of the blade without cutting the inner wire insulation.

Claims

Claims 1 The claim is made for a knife used to cut the outer sheaths of

electrical cable where due to the geometry and dimensions of the knife the path which is closely followed by the point at the end of the cutting blade during the cutting depth adjustment of the blade is angled between 200 and 30 to a normal line which is at 900 to the main cutting edge of the blade and is defined as a and where the cutting face which rests on the cable during the longitudinal cutting of the outer sheath the electrical cable is at an angle 90 -ct from the line of the path followed by the point of the blade.

2 A knife according to claim 1 where the blade-carrier which holds the blade is attached to the main body of the knife by a flexible strip which is either integral with the blade-carrier or a separate flexible strip.

3 A knife according to claims I and 2 where the length of the exposed blade used for cutting the cable sheath in a circumferential direction and the radius from the point on the flexible strip where the blade-carrier flexes to the mid point of the exposed blade has a ratio of 1:4 or greater.

4 A knife according to claims 1 and 2 and 3 where the radius from the point on the flexible strip where the blade-carrier flexes to the point of the blade used for cutting the cable sheath in the longitudinal direction is such that the radial path followed by the point of the blade describes an arc that cuts the path described in claim 1 at the points of minimum and maximum exposure of the blade point and the cord between these points of minimum and maximum exposure coincides with the path described in claim 1.

A knife according to all preceding claims where the radius from the point on the flexible strip where the blade-carrier flexes to the point of the blade used for cutting the cable sheath in the longitudinal direction is of a length greater than 120mm.