US3805382A

US3805382A - Coaxial cable slitter

Info

Publication number: US3805382A
Application number: US00333007A
Authority: US
Inventors: N Benedict
Original assignee: Ajax Tool Works Inc
Current assignee: Ajax Tool Works Inc
Priority date: 1971-06-17
Filing date: 1973-02-16
Publication date: 1974-04-23
Anticipated expiration: 1991-04-23

Abstract

A cutting tool usable with a pneumatic hammer or the like is provided to slit an outer sheath of a cable having metal and plastic layers in the sheath. An upper guiding surface is provided on a forward end of the tool for sliding along the outer surface of the cable. A cutting web projects inwardly from the upper guiding surface to slit the sheath. A shoe is provided on the inward end of the cutting web to slide along an inner base layer covering internal conductors to prevent inward movement of the cutting edge and damage to the internal conductors. Slit edges of the sheath flow through the channels formed between the upper guiding surface and the top surface of the shoe. Means are provided on the tool to prevent its turning in the hammer and this aids in guiding the tool and making a straight line cut. A cutting edge may be provided on the tool to cut a layer of the sheath underlying the shoe.

Description

United States Patent [191 Benedict, Jr.

[ COAXIAL CABLE SLITTER [75] Inventor: Neil W. Benedict, Jr., Evanston, Ill.

[73] Assignee: Ajax Tool Works, Inc., Franklin Park, Ill.

[22] Filed: Feb. 16, 1973 [21] Appl. No.: 333,007

l lelated US. Application Data [63] Continuation-impart of Ser. No, 154,140, June 17,

1971, abandoned.

[52] US. Cl 30/90.4, 130/925, 30/286 [51] Int. Cl B26b 27/00 [58] Field of Search 30/90.4, 92.5, 168, 277, 30/294, 286

[56] References Cited UNITED STATES PATENTS 3,577,638 5/1971 Chandler 30/168 2,616,172 11/1952 Parker 2,559,387 7/1951 Baker 3,162,945 12/1964 Stabs.....

1,611,574 12/1926 Armbruster.

3,698,085 10/1972 Ray 30/90 4 [451 Apr. 23, 1974 Primary Examiner0thell M. Simpson Attorney, Agent, or FirmFitch, Even, Tabin & Luedeka [5 7] ABSTRACT A cutting tool usable with a pneumatic hammer or the like is provided to slit an outer sheath of a cable having metal and plastic layers in the sheath. An upper guiding surface is provided on a forward end of the tool for sliding along the outer surface of the cable. A cutting web projects inwardly from the upper guiding surface to slit the sheath. A shoe is provided on the inward end of the cutting web to slide along an inner base layer covering internal conductors to prevent inward movement of the cutting edge and damage to the internal conductors. Slit edges of the sheath flow through the channels formed between the upper guiding surface and the top surface of the shoe. Means are provided on the tool to prevent its turning in the hammer and this aids in guiding the tool and making a straight line cut. A cutting edge may be provided on the tool to cut a layer of the sheath underlying the shoe.

8 Claims, 8 Drawing Figures ammn APR 2 3 19w. :3 8 O5; 3 82 SHEET 1 UF 2 FIGJ INVENTOR NEIL W. BENEDICT, JR.

En, 66. mm, limb ATTYS.

1 COAXIAL CABLE SLITTER This application is a continuation-in-part application of co-pendingapplication Ser. No. 154,140 entitled Cutting Tool filed June 17, 1971 now abandoned.

This invention relates to a cutting tool for use with a reciprocating hammer or the like and more particularly to a tool for cutting or slitting a multi-layered sheath of a cable having a large number of electrical conductors within the sheath.

The cutting tool will be described in connection with the slitting of sheaths of large diameter telephone cables of the Stalpeth, Qualpeth or other kinds in which the sheath is comprised of an outer layer of plastic and one or more internal metal layers usually of corrugated aluminum, lead or steel. Inside the metal layer is a base layer such as a spiral wrapping of paper surrounding bundles of individual electrical conductors. When slitting outer plastic and metal layers in a cable called CCW, the base layer is a second inner layer of plastic which covers another, second internal corrugated metal layer. In armored cables of this kind, the plastic layer or layers protect against intrusion of moisture and the metallayer or layers protect against gnawing rodents. i

The plastic and metal layered sheath is particularly difficult to slit and open with power driven cutting tools because of the danger of cutting into the base layer or through the base layer and severing the individual conductors. Commonly any such slitting is done with manual tools. However, this is slow and difficult work particularly when the slit needs to be made for an extended length, e.g., feet or more.

More specifically, such long slits may be required prior to severing the cable to the exact length required and splicing its conductors to the conductors of another cable. Within the cable, there are often individual conductors which are faulty and which are suitably marked at a cable end prior to capping the cable end. When splicing such a cable into an existing cable line, the end cap is removedand the faulty conductors are located. However, before severing the cable to the exact length desired for the slice, it is necessary to be able to trace and retain the identity of the faulty conductors to the point of severing. I

Thus, it is often common practice to manually slit the outer sheath of the cable for 10 to feet and to trace the defective conductors through this length to the location at which the cable is to be severed to its final length. In addition to being extremely slow, presently used manual methods of slitting the metal sheath layer result inrough and ragged edges on the slit metal; and

this rough metal edge cuts the fingers of the workers when they try to spreadthe metal layer without use of tools.-- 'w One particular difficulty of developing an adequate, power driven tool for slitting such a multi-layer sheathed cable is that of maintaining a substantially constant depth of penetration of the tool so that it does not dig into the base layer. Also, where the base layer is a paper wrap, the tool has a tendency to penetrate through the paper layer particularly as the paper layer is usually helically wrapped about the conductors, it has a series of helical edges exposed for engagement by the cutting tool as it moves longitudinally along the cable. Whenthe tool penetrates beneath one of the edges of the helical paper wrap, there is a tendency for the tool to dig in and penetrate deeper and to cut the conductors. On the other hand, the outer metal and plastic layers resist cutting and tend to force the cutting edge of the tool upwardly from the paper layer with the result that the slit is not made completely through the layers of the sheath. In addition to resisting these tendencies to dig in or to ride up and out of the slit, it would be desirable that the tool form a more smooth cut edge on the metal layer to prevent nasty cuts to the fingers of the workers spreading the sheath.

In a still further embodiment of the cable, the internal conductors are protected by a multi-layered sheath including an outer plastic layer and one or more internal metal layers such as a lead'layer and within the lead layer is a thick strong plastic base layer disposed about the electrical conductors. In such a cable, it is particularly desired not only to sever the outer plastic and metal layers but also to cut or to slit the internal thick plastic base layer without damage to the internal electrical conductors. In accordance with a further embodiment of the invention, a tool is provided which not only slits the multi-layered sheath but also forms a partial slit or cut in the plastic base layer whereby the plastic base layer may be readily removed as with the use of a further tool.

Additionally, it is preferred that the tool make a long straight slit rather than a curved or spiral slit as may occur if the tool is allowed to follow the curvature of the bundles of the internal conductors which are laid with a long turn in the cable.

Accordingly, a general object of the invention is to provide improved cutting tools, of the foregoing kinds.

Other objects and advantages of the invention will become apparent from the detailed description taken in connection with the accompanying drawings in which:

FIG. 1 is a perspective viewof a cutting tool embodying the novel features of the invention and driven by a conventional hammer to slit longitudinally a multi layered sheath of a cable;

FIG. 2 is a side elevational view of the cutting tool embodying the novel features of the invention;

FIG. 3 is a fragmentary bottom view of a cutting section of the tool of FIG. 2;

FIG. 4 is a cross-sectional view taken substantially along the line 4-4 of FIG. 1;

FIG. 5 is a cross-sectional view of a cutting web for the tool of FIG. 1;

FIG. 6 is a perspective view of a tool constructed in accordance with a further embodiment of the invention;

FIG. 7 is a fragmentary bottom view of a cutting section of the tool of FIG. 6; and

FIG. 8 is a cross-sectional view of a cable being cut with the tool of FIG. 6.

As shown in the drawings for purposes ofillustration,

the invention is in a first embodiment thereof embodied, very generally, in a cutting tool 11 for slitting a cable 13 of the Stalpeth or Qualpeth etc. kind which has an outer multi-layered sheath 15 surrounding an inner base layer such as a paper wrapping 17 which encircles and covers hundreds of individual electrical conductors 19. To form a longitudinally extending slit 21 in the multi-layered sheath 15, it is necessary to sever an inner encircling sleeve or layer 23 of metal usually steel or aluminum and an outer waterproof sleeve or layer 25 of plastic or elastomeric material ger of damaging the internal conductors 19. Additionally, the manual slitting has resulted in jagged sharp edges at slit edges 28 of the metal layer 25 which cuts workers fingers when they tried to spread the sheath 15.

In accordance with the present invention, the cutting tool 11 is constructed to move along a path at a substantially constant depth to sever the multi-layered sheath 15 without digging into the cable and injuring the internal conductors as the tool is pushed forward by a power driven hammer 30. To this end, the cutting tool is formed with a shoe 31 having a lower surface 33, as best seen in FIG. 4, for sliding along the top of the base layer and a blunt leading end for preventing digging in of the tool into the internal conductors. An upper or guiding surface 35 on the shoe 31 slides along the inner side vof the metal layer and prevents the tool from riding up and out of the slit. The shoe also defines the lower sides of a pair of channels 39 through which the slit sheath material flows. More specifically, the sheath being slit flows through the channels 39 formed between shoe guiding surfaces 35 and upper guiding surfaces 40 spaced therefrom and in a plane substantially parallel thereto. A thin cutting web 43 extends between the shoe 3] and the guiding surface on a body 44 for the tool. A sharpened leading and cutting edge 45 on the web 43 slits metal sleeve easily in along pass or passes which result in a less jagged edge 28 for the slit metal than heretofore experienced. Thus, the operator will not so easily cut his fingers when grasping and spreadingthe slit sheath. 7 f

Also, in accordance with the invention, the cutting tool 11 is made from a single piece of metal and is provided with means to prevent the turning of the tool during a slitting operation. The tool has a tendency to rotate and follow one of the long helical grooves (not shown) resulting from the twist in bundles of conductors l9 laid in the cable. The paper wrapping covers these grooves but the contour is still there and would be followed by shoe 31 except that means in the form of retaining grooves 50 on the tool body 44 are in engagement with balls in a retainer 47 to prevent turning of the tool.

Referring now in greater detail to the cutting tool 11, his formed with an elongated body 44 with a reduced diameter shank 51 at one end for attachment to a pneumatic hammer or the like. The preferred tool 11 is made of forged and heat treated steel with a generally circular cross section with the shoe 31 and cutting web 43 integrally formed on the end of the tool body opposite the shank 51. By way of example, the illustrated cutting tool 11 may have an overall length of 8 inches and a maximum diameter of five-eighths inches with the shank 51 machines to a 0.400 inch diameter.

As shown in the drawings in FIG. 1, the cutting tool 11 will be held at an angle to the longitudinal dimension of the cable 13 while the slit is being formed therein and the cutting tool is receiving a series of reciprocating blows from the hammer 30 which is a pneumatic air hammer in this instance. With the cutting tool at the inclination shown in FIG. 1', the bottom surface 33 of the shoe 31 is riding along the top of the paper wrapper 17, as best seen in FIG. 4, in a plane substantially parallel to the longitudinal axis of the cable. When the shoe 31 is riding on the paper wrapping and the cutting web 43 is slitting, the upper guiding surface 40 will be sliding along the top surface of the cable and also helping in preventing the digging in of the shoe into the conductors l9.

The upper guiding surface 40 for sliding along the outside of the cable is formed at an angle A to a longitudinal axis 55 of the elongated body 44 of thecutting tool. By way of example only, the angle A in the illustrated cutting tool is 30. As the shoe guiding surface 35 is preferably parallel to this guiding surface 40, it is also at a 30 angle to the longitudinal axis and hence, the channels 39 defined therebetween are also at an angle of 30.

The height of the channels 39 through which the slit multi-layers of sheath flow is chosen so that the sheath will slide readily between the

surfaces

35 and 40 without binding and will substantially fill the height of the channels. Good results have been obtained with the channels having a three-sixteenths inch height between the guiding

surfaces

35 and 40, and this has been found to accommodate sheaths of a large number of commercially used cables. Where the cable has a sheath which is either much thicker or much thinner; then the tool is provided with another and appropriately dimensioned channel height. The cables often come with different thicknesses of metal for its metal sleeve, for example from 6 mil to l6 mil corrugated sleeves and in some instances the sheath includes two metal sleeves. The corrugations in the metal sleeves run circumferentially about the cable conductors 19 rather than longitudinally.

The cutting web 43 is preferably ground to have a thin pointed leading cutting edge 45; and preferably the web is relatively thin in cross section, e.g., about onesixteenth inch in thickness. The illustrated web 43 is formed by a milling of a front end of the tool body 44 with milling cutters (not shown) cutting the channels 39 from a blunt front wall 60 for the tool body to a rearward location at its side wall while at an angle A. The cutting edge 45 of the web is then milled to be substantially normal to the

surfaces

35 and 40 and to be about one-eighth inch rearward of a blunt leading edge 69 of the shoe. The projection of the leading edge 69 of the shoe 31 forward of the cutting web 43 is useful at the initial start of the slitting operation as it may be inserted into a groove within a corrugation of the metal layer to position the shoe at, the proper depth when making the initial slit at one end of the cable.

Easier slitting is obtained when the web cutting edge 45 is perpendicular to the guiding surfaces 35 and 40 rather than be sloped at an acute angle to one of these surfaces. That is, if the cutting edge 45. is sloped forwardly or rearwardly, the material being slit is then driven upwardly or downwardly, depending on the direction of the slope, and flows less freely through the channels 39. This driving of the material upwardly or downwardly has been found to slow down the slitting operation.

To facilitate sliding of the shoe 31 over the paper wrapping 17, it is preferred to curve its lower surface 33; and this is accomplished by grinding away metal from along the edges of the shoe to form a central thicker domed portion at the center of the shoe bottom surface 33. A trailing heel 65 for the shoe 3] is also ground and rounded at its intersection with rear wall 67 of the web 43 to provide a heel about which the tool can be rocked so as to change the inclination of the tool and thereby raise or lower a leading edge 69 for the shoe to assure slips over helical edges 71 (FIG. 1) of the paper wrapping 17.

This leading edge 69 of the shoe 31 is flat and wide, as best seen in FIG. 3, rather than pointed to facilitate its sliding without digging into the paper therebeneath or the sheath thereabove. In the same manner, the upper leading end wall 60 of the tool is also flat, blunt and wide to prevent digging into the outer surface of the plastic layer of the cable.

The illustrated shoe 31 is formed with parallel sides 75 which are in this instance separated from each other by about 0.250 inch. Thus, the width of the shoe surface 31 is about one-fourth inch while the upper guiding surface 40 has a maximum dimension of about ninesixteenths inch. Due to the manner of formation of the tool, the flat

leading end walls

60 and 69 are substantially aligned with each other in a plane perpendicular to the longitudinal axis 55 of the cutting tool. The leading edge 45 of the cutting web 43, however, is disposed about one-eighth inch rearward of the inclined to the flat edge 69 of the shoe.

To prevent turning of the shank 51 in the retainer 47 and a consequent curved slit 21 for the sheath 15, the tool 11 is provided with four retaining grooves 50 on its outer peripheral wall. The retaining grooves are elongated and substantially longitudinally directed to receive therein retainer balls of the conventional retainer 47. These balls hold the tool body. 43 against rotation due to the shoe 31 trying to follow a generally helical groove formed by the lay of a group of conductors.

That is, the conductors within the cables are often grouped into bundles which have a helical lay which provides a slight contoured surface for the paper wrapping 17 which the tool has a tendency to follow. The retaining grooves 50, however, prevent this turning movementof the tool causing the straight line slit 21 whichis most desirable particularly over a long length of cable, for example to feet.

As an aid to understanding the invention, a brief description of one use of the illustrated tool 11 will be given. When providing a length of cable between two points, the cable is often selected to have a length slightly larger than the length estimated the cable would eventually take. This is necessary so that the cable, once installed, is never too short to form the splice. The multi-wire telephone cable 13 illustrated often is manufactured with several defective conductors 19 therein which are tagged at the factory prior to receiving an end cap. When the end cap is removed,,the tagged wires may be seen. To enable tracing of the defective wires from the capped end of the cable for 10 or 15 feet to the point at which the cable is to be severed to the exact length needed, requires that the cable be slit and the'wires traced.

To slit the cable 13, the cutting tool 11 is inserted cable. At the proper angle, the lower guiding surface 33 of the shoe slides forwardly across the edges 71 of the paper wrapping 17 with the leading edge 69 of the shoe moving forward past the edges 71 of the wrapping. The tool is prevented from moving generally upward by the engagement of the shoe surface 35 against the underside of the metal layer 23. On the other hand, the tool does not tend to dig in because of the shoe surface 33 sliding on the paper layer 17 and also because the upper guiding surface 40 is sliding along the outer surface of the cable. The cut material on both sides of the cutting web 43 flows through the channels 39, as best seen in FIG. 4.

The operator may move the tool 11 quite rapidly through the cable sheath 15 with a minimum of time and manual effort as contrasted to the prior art manual operation. When reaching the desired slit length, the tool may be removed. It has been found that the cut edges 28 of the corrugated metal sleeve are not nearly as rough as that achieved with the prior art device and that the slit 21 may be expanded with less possibility of cutting ones fingers.

The cutting tool has been described herein principally in connection with the slitting of Stalpeth or Qualpeth cables but it isequally usable with various other cables such as the CCW cable (not shown) which has an outer layer of plastic, a layer of corrugated metal, a second inner layer of plastic, 3. second inner layer of corrugated metal, a thin wrapping layer of paper or plastic tape, and internal conductors. When slitting this CCW layer, the base layer on which the bottom surface 33 of the shoe 31 slides is the second layer of plastic which, of course, is not readily penetrated as the paper base layer of the Stalpe-th and Qualpeth cables. However, the problems of severing the outer plastic and metal layers with the cut being made at a substantially constant depth are still present. Thus, it will be seen that with shoe sliding along the base layer, the layers thereabove may be easily and readily severed in the CCW cable as in the illustrated cables.

In accordance with a further embodiment of the in vention, a cutting tool generally similar to that described above in connection with FIGS. 1-5, will now be described with common reference characters, but having a suffix a added, to designate elementside'ntical to elements of the tool 11 above described. More specifically, for cutting an inner thick plastic base layer of a sheath 15a for a cable 13a (FIG. 8), the cutting tool 11a is provided with a lower slitting blade having a cutting edge 81 which preferably forms orcuts a longitudinally extending slit 83 in the base layer 80 as the cutting web 43a forms the longitudinally extending slit 21a in the layers of the cable sheath thereabove. Preferably, the slit 83 is not cut completely through the plastic base layer 80 to a plurality of small insulated electrical conductors 85 which are spiraled about the cable and laid beneath the plastic layer 80. In the illustrated cable l3a, the conductors 85 are covered by an encircling thin nonwoven layer 87 formed of plastic filaments, which layer is interposed between the plastic base layer 80 and the conductors 85. The thin nonwoven layer 87 lacks sufficient depth or strength to rely on its acting as abarrier to prevent the cutting into the conductors 85 if one should make the knife edge 81 of sufficient depth to cut completely through the plastic base layer 80. Before describing the preferred knife edge 81 in more detail, the illustated cable 13a will be described in greater detail.

The illustrated cable 13a is approximately 3% inches in diameter and formed with an outer plastic sheath layer 82 covering and encircling steel layer 89 which is formed by spirally wrapping a thin steel band about an adjacent metallic layer 91 formed of cast lead, in this instance and having a thickness of about threesixteenths inch. The lead layer 91 is solid and not wound. Preferably, a tar or sticky asphalt-like material layer 93 is interposed, between the steel layer 83 and the lead layer 91 and a similar tar layer 94 is disposed between the plastic layer 82 and the steel layer 89. Between the lead layer 91 and the plastic layer 80, there may be additional thin plastic spirally wound paper layers 95.

In addition to the small encircling electrical conductors 85, the cable 13a carries fifteen coaxial conductors 99 arranged an outer ring and, separated by a thin nonwoven layer 101 formed of plastic filaments from an inner ring of eight coaxial conductors 99. Each of the coaxial conductors 99 is comprised of a central solid copper conductor 103 about which are placed a series of longitudinally spaced plastic disks 105. About the outer surfaces of the plastic disks are encircling copper tubes 107 and spirally wrapped about each of the copper tubes 107 is a steel band 109. At the center portion of the cable 13a, there are a plurality of small insulated conductors 110 which are wrapped with a thin nonwoven layer 111 formed of plastic filaments. In the insterstices between the inner and outer rings of coaxial conductors 99 are inserted pairs of small insulated electrical conductors 113.

Turning again the tool 11a, the respective channels 39a in the tool 11a are slightly wider than the channels 39 for the above described tool 11 because as the sheath layer a to be slit by the cutting edge 45 is thicker than the sheath layer 15 for the cable 13. In this instance, the sliding or upper guide surface a will slide along the top of the outer sheath layer 82 while the lower surface 33a of the shoe 31a slides along the outer surfaceof the plastic layer 80.

The preferred slitting or knife edge 81 is integral with the shoe 31a and projects downwardly from the lower guiding surfaces 33a of the shoe 31a. Preferably, the knife edge 81a is vertically aligned with the cutting web 43a and thus is centered to provide a straight longitudinal slit 83 aligned with the upper slit 21a so that the tool will not twist or tend to travel other than in a direction parallel to the longitudinal axis of the cable. By way of example only, the cutting edge 81 has been formed with a dimension of about 0.046 inch depth with the opposite side walls 115 converging and meeting at a longitudinally extending apex 117. Preferably, thev opposite side walls 115 are at angles of to the vertical and defined therebetween an included angle of 90. Of course, other dimensions and angular relationships may be used depending upon the thickness of the underlying layer 80.

In this instance, the slitting edge 81 extends the full length of the lower surface of the shoe 310, but in other instances a leading point 120 on the slitting edge 81 was positioned about one-sixteenth of an inch rearwardly of the blunt end 69a for the shoe. Also, it is preferred that this leading point 119 of the slitting edge 81 be ground to provide a slightly sharpened point for facilitating the slitting of the plastic layer 80. After form ing the slit 83 in the plastic layer 21a, a person may take a conventional knife or hand tool having a pointed edge and finish slitting the plastic layer by cutting further into the plastic layer along the straight line slit 83. As the plastic layer 80 may be under some tension to widen the slit 83, the final manual cut through layer is relatively easy. Of course, one must be careful not to snag or cut one of the underlying conductors 85.

From the foregoing it will be seen that the present invention provides a new and improved cutting tool which is particularly useful for quickly and efficiently forming elongated longitudinal slits in a sheathed cable with the tool cutting the sheath while moving at a substantially constant depth of penetration. Thus, the interior conductors in the cable will not be damaged.

While a preferred embodiment has been shown and described, it will be understood that there is no intent to limit the invention by such disclosure but, rather, it is intended to cover all modifications and alternate constructions falling within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A one piece, integral cutting tool for slitting a sheath of a cable having an interior base layer surrounding a plurality of wire conductors, said tool comprising an elongated body having a longitudinal axis, a shank end on a rear portion of said body for connection to a reciprocating hammer, a cutting section on a forward end of said body for slitting said sheath, an upper guiding surface formed at an angle to said longitudinal axis at said cutting section for sliding movement along an outer surface for said sheath, a cutting web projecting from said upper guiding surface and extending inwardly for slitting the sheath, a leading cutting edge on said web facing in a forward direction, a shoe on the inward side of said cutting web for limiting the radially inward movement of said cutting edge, said cutting web supporting and connecting said shoe to said body, a lower guiding surface on said shoe for riding on the base layer, a blunt leading end on said shoe for preventing digging and inward penetration of said tool toward the conductors, and an upper surface on said shoe projecting laterally from and on opposite sides of said web and defining open channels with said upper guiding surface through which channels the slit sheath edges pass freely as said cutting tool moves forward.

2. A cutting tool in accordance with claim 1 in which said shoe is disposed at substantailly the same angle to the longitudinal axis as said upper guiding surface is disposed thereto.

3. A cutting tool in-accordance with claim 1 in which said upper guiding surface is a substantially larger surface than said upper surface of said shoe, said guiding surface and said upper shoe surface being substantially parallel to each other.

4. A cutting tool in accordance with claim 1 in which means on said shank end of said body prevents turning of said tool relative to said hammer while slitting.

5. A cutting tool in accordance with claim 1 in which a rounded heel is formed at a rearward portion of said shoe to facilitate rocking of the tool to change the radially inward position in said cable of said flat, leading edge of said shoe.

6. A cutting tool for slitting a sheath of a cable having an interior base layer surrounding a plurality of wire conductors, said tool comprising an elongated body having a longitudinal axis, a shank end on said body for connection to a reciprocating hammer, a cutting section on the other end of said body for slitting said sheath, an upper guiding surface formed at an angle to said longitudinal axis at said cutting section for sliding movement along an outer surface for said sheath, a cutting web projecting from said upper guiding surface and extending inwardly for slitting the sheath, a leading cutting edge on said web, a shoe formed on the inward side of said cutting web for limiting the radially inward movement of said cutting edge, a lower guiding surface on said shoe for riding on the base layer, an upper surface on said shoe projecting laterally from and on opposite sides of said web and defining channels with said upper guiding surface through which pass the slit sheath edges as said cutting tool moves forward, and a cutting edge on said tool projecting below said lower guiding surface of said shoe to slit at least partially the base layer of said sheath.

7. A cutting tool in accordance with claim 6 in which said cutting edge projects downwardly from and is integral with said shoe, said cutting edge being in vertical alignment with said cutting web.

8. A cutting tool in accordance with claim 7 in which said cutting edge is formed with inclined surfaces converging to a lower pointed, longitudinally extending edge.

Claims

3. A cutting tool in accordance with claim 1 in which said upper guiding surface is a substantially larger surface than said upper surface of said shoe, said guiding surface and said upper shoe surface being substantially parallel to each other.