The present invention relates to an apparatus for cutting a hole through the wall of a tube or similarly curved structure.

There are many circumstances in which it is desirable to be able to cut a hole in a structure the outer surface of which is generally cylindrical. For example, it is often necessary to cut a hole into an existing underground pipe to make a branch connection to that pipe. It is a relatively easy matter to cut such a hole using a tubular cutting tool mounted on a drive assembly that itself is securely mounted on the pipe to be cut. Given the curvature of the pipe surface, however, such a cutting tool must project a considerable distance into the interior of the pipe.

Several of the most recent pipe rehabilitation tec. -r.iques involve the insertion of a close fit or tight fit plastic lining , generally of polyethylene or PVCu. There are mechanical fittings for making branch connections to such lined pipes which can be fitted by drilling straight through pipe and liner, but many Utilities prefer the use of welded connections which offer several advantages. This requires that access be gained to the liner, and moreover that such access be gained without cutting into the liner itself.

Because of the curvature of the pipe surface, it is not possible to cut a hole in a lined pipe using a simple tubular cutting tool without also cutting into the liner. Accordingly it has become conventional practice to cut a hole in the existing pipe by cutting two parallel straight slots in the pipe wall in a direction parallel to the pipe axis and then to cut two circumferential slots which are spaced apart in the axial direction and each lie in a plane perpendicular to the pipe axis, the ends of the circumferential slots intersecting the ends of the axial slots. This can be achieved using a simple cutting apparatus the depth of cut of which can be accurately controlled. Unfortunately when this approach is adopted the result is a hole in the existing pipe which has square overcut corners. -\ ^' hen pressure is subsequently applied to the liner, stress is concentrated in the pipe at these overcut and hence weakened corners, so that stress cracks can be readily initiated. Accordingly it is apparent that holes cut in the wall of a lined pipe should have arcuate edges of maximum

possible radius so that stress concentration is minimised. Unfortunately no practical apparatus for cutting such a hole is currently known whicn does not damage the liner.

It is an object of the present invention to obviate or mitigate the problem outlined above.

According to the present invention, there is provided an apparatus for cutting a hole through a curved wall of a structure, comprising a cutting tool drive assembly adapted to receive a cutting tool and to rotate the cutting tool about a predetermined cutting axis, and a support for the drive assembly which in use is secured in a predetermined orientation relative to the structure to be cut, the drive assembly being movable relative to the support about a support axis which intersects a point on the structure which is central to the position in which the hole is to be cut, the support axis being substantially perpendicular to the surface of the structure at the point of intersection, wherein the drive assembly is mounted on the support by a linkage which enables the drive assembly to move relative to the support so as to vary the inclination of the cutting axi s relative to the support axis, and the apparatus comprises a head which is located adjacent the cutting axis and in use bears against the surface of the structure to determine the spacing between the surface and the drive assembly, the geometry of the linkage being such tnat as the drive assembly is moved about the support axis the head follows the curved surface of the structure and the cutting axis is : - -intained substanti ally perpendicular to the surface of the structure wnere it is intersected by the cutting axis.

Assuming that the structure is a tube, the support axis will be arranged perpendicular to the tube axis and the drive assembly linkage will be arranged such that the cutting axis is always s _^ ostantially perpt . -_lar to the t _-. e axis. Thus, simply by rotating the drive assembly around the support axis a hole may be cut in the tube the edge of whicn hole is continuously curved. Thus the hole does not define any corners at which excessive stress would be concentrated.

Preferably, the support comprises a support member that is linked to the drive assembly by first and second links, each link being pivotally connected to the support member and to the drive assembly

so as to permit movement of the drive assembly in a radial direction relative to the support axis. The support member may define two spaced apart limbs, the first link being defined by a first arm pivotally supported between the two limbs, and the second link being defined by two arms pivotally supported on the limbs on opposite sides of the first arm. The head may be defined by at least one projection formed on one of the links. Preferably the link defining the head supports two spaced apart limbs located on opposite sides of the cutting axis, each limb of the link supporting a projection to define the head. Alternatively, the head may be defined by a member extending from the drive assembly.

Preferably the support member is spring mounted on a support frame so as to be biassed against the structure to be cut.

The drive assembly may comprise a cutting tool support mounted on a drive assembly frame, the cutting tool support being displaceable relative to the drive assembly frame. The drive assembly may comprise a tool drive motor which is displaceable with the cutting tool support. The drive assembly may comprise a pair of spaced apart plates between which the motor is supported.

Preferably the drive assembly is secured to a support frame which in use is clamped to the structure to be cut by a telescopic cross arm. Such an arrangement enables the displacement of the support axis relative to the support frame.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is a side view of an apparatus in accordance with the invention mounted on a lined pipe;

Fig. 2 is a view of the apparatus cf Fig. 1 in the direction of lines 2-2 after rotation of a drive assembly of the apparatus relative to the support through 90°;

Fig. 3 is a plan view of a support member in the form of a support block incorporated in the apparatus of Figs. 1 and 2;

Figs. 4 and 5 are respectively views on the lines 4-4 of Fig. 3 and 5-5 of Fig. 4;

Fig. 6 is a plan view of a first link incorporated in the apparatus of Figs. 1 and 2;

Figs. 7 and 8 are respectively views on the lines 7-7 of Fig. 6 and δ-8 of Pig. 7:

Fig. 9 is a side view of one of two second links incorporated in the apparatus of Figs. 1 and 2;

Fig. 10 is a view of the second link of Fig. 9 in the direction of lines 10-10;

Fig. 11 is a perspective view of a drive assembly of a second embodiment of the invention;

Fig. 12 is an exploded view of the drive assembly of Fig. 11; and

Fig. 13 schematically illustrates the structure of a support for the drive assembly of Figs. 11 and 12.

Referring to Figs. 1 and 2. the illustrated apparatus is shown mounted on a pipe 1 lined with a polyethylene liner 2. The apparatus comprises a support frame in tne form of an inverted U-shaped support memcer J that is clamped by means, not shown, to the pipe 1. Vertical support legs 4 extend from the support member 3 and in turn support a cross arm 5.

The cross arm 5 supports a fixed tube 6 in which a tubular shaft 7 is slidably received. A support block 8 is mounted on the bottom end of tne shaft 7. A collar 9 is secured to the shaft 7 and a spring 10 is compressed between the collar 9 and the underside of the fixed tube 6. Thus the spring 10 biasses the support block downwards against the upper surface of the pipe 1. A hand wheel 11 is secured to tne upper end of the shaft 7 to enable the shaft to be rotated about a support axis indicated by line 12.

A drive assemoiy is linked to tne support block 8 by a first link h and a pair of second links 14. The first link 13 is pivotally connected to block 8 by a pivot pin 15 and is pivotally connected to the drive assembly by a pair of axialiy aligned pivot pins 16. Each .i tne pivot h.;- - .' runted in =. res f'.ive one of a pair of spaced apart plates 17. or v one of the plates 17 oeing shown in the drawings. Tne second links 14 are pivotally connected to the block 8 by a pair of axialiy aligned pivot pins 18 and to the plate 17 by a pair of axialiy aligned pivot pins 19. Only one of the second links 14 is visible in the drawings.

A motor 20 is supported between the plates 17, the motor being intended to receive a cutting tool 21 and to rotate that cutting tool

about a cutting axis indicated by line 22. The motor is mounted on a cross plate 23 which is suspended from a cross plate 24 secured to the plates 17. The cross plate 23 is suspended on a pair of rods 25, both of which are freely slidable relative to the cross plate 24. A knurled nut 26 is mounted on a threaded portion of one of the rods 25, rotation of the knurled nut 26 enabling the spacing between the plates 23 and 24 to be adjusted. This adjustment controls the depth of penetration of the cutting tool into the tube 1. A bronze bushed steady bearing 27 is secured between the plates 17 and maintains the stability of the cutting axis 22 relative to the drive assembly.

Referring to Figs. 3 to 5, the detailed structure t: the supper: block 8 is shown. The block defines a blind bore 28 which receives the lower end of the shaft 7 and is secured to the shaft by a pin ( net shown) inserted through threaded bore 29. Threaded b res 30 receive the pivot pins 15 (Fig. 1) and threaded bores 31 receive the pivot pins 18 (Fig. 1).

The bores 31 are supported on the outside surfaces of a pair of limbs 33. The first link 13 is accommodated between the limbs 33. Details of the first link are shown in Figs. 6, 7 and 8.

Referring to Figs. 6 to 8, the first link is in the form of a flat plate 34 defining a pair of limbs 35 from which projections 36 extend. The plate defines bores 37 which receive the pivot pins 15 (Fig. 1) and bores 38 which receive the pivot pins 16 (Fig. 1). The projections 36 define curved lower surfaces 39 which in use rest against the upper surface of the pipe 1 (Fig. 1) and between which the cutting axis 22 (Fig. 1) extends. Thus the surfaces 39 define a head wr.ier- determines the spacing between the cutting assembly and the pipe 1.

Referring to Figs. 9 and 10, the illustrated link 14 defines a bore 40 which receives the pivot pin 18 (Fig. 1) and a bore 41 which receives the pivot pin 19 (Fig. 1).

Fig. 2 shows the apparatus after rotation of the hand wheel 11 through 90° as compared with the view of Fig. 1. It will be seen that given the freedom of movement afforded by the linkage defined by links 13 and 14, the drive assembly is free to swing away from the support axis 12 in a radial direct ^' n relative to that axis. The only constraint on the freedom of , . ement of the driλ'e assembly is contact between the projections supported by the link 13 which bear

against the outer surface of the pipe 1 on either side of the cutting axis 22. Thus as the hand wneel 11 is turned away from the position shown in Fig. 1 the drive assembly swings away from the support axis 12 until the hand wheel 11 has been rotated through 90°. Further rotation of the hand wheel will then cause the drive assembly to be swung back towards the support axis 12. This motion ensures that the cutting axis 22 is always substantially perpendicular to the axis of the pipe 1 and to the pipe surface being cut. The precise inclination of the cutting tool axis will depend on the geometry of the linkage, and may vary by a few degrees as the drive assembly is rotated around the axis 12. Such variations will not vary the depth of cut significantly however and therefore can be readily accepted.

Assuming that the apparatus is initially positioned as shown in Fig. 1, the cutting tool is lowered into contact with the outer surface of the pipe by adjustment of the nut 26. The drive motor is then started and the cutting tool is lowered further by adjustment to the nut 26 until the cutting tool has penetrated the full depth of the pipe wall. Lowering of the cutting tool is terminated before any significant penetration of the liner 2 occurs. Once the cutting tool has penetrated through the full depth of the pipe wall, the hand wheel is slowly turned and the cutting tool then cuts out a slot in the pipe wall the depth of which is accurately maintained so as to avoid damage to the liner 2. Fig. 1 shows a slot 42 which would be cut in the pipe wall after rotation of the hand wheel 11 through in excess of 180" . After rotation of the hand wheel 11 through 360 ^c a coupon of metal can be removed leaving a clean hole in the wall of the pipe 1 and an intact liner 2 extending beneath that hole. An appropriate connection can then be made to the liner 2 using conventional techniques. Given that the edge of the hole cut in the pipe 1 is smooth ^" : " ^urved there are no sharp corners to concentrate stress. Furthermore, by appropriately designing a coupling which can be. for example, adhered to the liner 2, all of the liner 2 around that coupling can be reliably reinforced by a curved flange on the coupling.

It will be appreciated that alternative design options could be adopted to those illustrated. For example, the hand wheel 11 could be replaced by a suitable worm gear arrangement to provide a constant

rate of rotation of the shaft 7 relative to the support axis 12. Alternative motor drive arrangements could be provided also, the only requirement being that the driven cutting tool is supported against transverse forces and that its depth of penetration can be accurately controlled. For example, rather than supporting a milling cutter or the like in a chuck which runs in a steady bearing with the motor being movable relative to that bearing, the main bearing for the tool may itself be movable relative to the drive assembly such that the motor moves with the bearing. This could be expected to achieve greater rigidity increasing the working life of the milling cutters, an removing the cutting load from the motor bearings.

It will be noted from Figs. 1 and 2 that the collar 9 defines a bore 43. This bore is provided to enable a compression spring to be fitted between the collar 9 and a suitable position on the drive assembly or the linkage so as to increase the force with which the cutting tool bears against the pipe. The compression spring device is not shown in the drawings simply to make it easier to see the basic components of the structure. It will of course be appreciated that an alternative pressure applying device powered, for example, from a compressed air supply used to drive the motor 20, could be used as an alternative to a compression spring device.

Referring to Figs. 11 to 13, a second embodiment of the invention will now be described. The drive assembly of the second embodiment is illustrated in Fig. 11, components of that assembly being shown in exploded form in Fig. 12.

The drive assembly comprises a frame defined by a pair ot spaced apart plates 42 between which an adjuster block 43 and a bottom block 44 are rigidly secured by bolts. A carrier block 45 is slidably received between the plates 42, each of the plates 42 being received in a respective slot 46 formed in opposite sides of the block 45. An arm 47 is secured by a bolt to the block 44. A threaded rod 48 is engaged in a bore 49 in the block 45 and an internally threaded hand wheel 50 is screwed onto the top of the rod 48. Rotation of the hand wheel 50 adjusts the position of the block 45 relative to the frame. Detents 51 are spring-mounted in the adjuster block 43 so as to engage releasably in a recess defined in the underside of the wheel 50. The detents hold the wheel 50 in selected positions at half-turn

intervals, each half-turn corresponding to a vertical displacement of the carrier block 45 of 0.5mm. A drive motor 52 is mounted on a support flange 53 which is bolted to the carrier block 45. The output shaft 54 of the motor extends through the carrier block 45 and the bottom block 44 to engage a chuck 55 supporting a cutting tool 56. A locater plate 57 is secured by bolts to the underside of the carrier block 45 and engages in a slot in the bottom of the rod 48 so as to prevent axial or rotational movement of the rod 48 relative to the carrier block 45.

Referring to Fig. 13, the lowermost portions of the drive assembly of Figs. II and 12 are shown mounted on a modified support assembly. The support assembly comprises a support frame 58, support legs 59, a cross arm 60, a fixed tube 61, a rotatable shaft 62, and a support block 63. The support block is connected to the drive assembly of Figs. 11 and 12 by a pair of outer links 64 and a single inner link 65. The outer links 64 are connected to pivots mounted on the support block 63 at one end and on pivots secured to bores 66 (Fig. 12) in the drive assembly frame. The inner link 65 is connected to bores 67 (Fig. 12).

The operation of the embodiment described with reference to Figs. 11 to 13 is much the same as that of the embodiment of Figs. 1 to 10. Thus, the depth of cut of the cutting tool 54 is controlled by rotation of the hand wheel 50 and the drive assembly is moved around the axis of the shaft 62 so as to cut the desired hole in the supporting pice. As the drive assembly turns relative to the shaft axis, the arm - 7 defines a head which rests on the surface of the pipe to be cut. and thus controls the position of the drive assembly in association with the pivotal links 64 and 65.

The support assembly of Fig. 13 differs from that of the embodiment ?: ^' Fi s. 1 to 10 in tw respects. Firstly, rotation of the shaft 6 is controlled by a hand wheel 68 which drives a worm meshing with a toothed wheel 69 secured to the shaft. This enables a much smoother rotational movement of the shaft, thereby improving the uniformity of the cut. In addition, the cross arm 60 is telescopic, comprising an outer tubular member rigidly supported by the support legs 59 within which an inner tubular member 70 is slidably mounted on slide bearings 71 and 72. Rotation of a hand wheel 73 linked to a

threaded shaft 74 received in a threaded formation mounted on tne component 70 enables the component 70 to be displaced to the le:t : n Fig. 13, components of the cross arm visible in Fig. 13 to the left : : line 75 being displaceable relative to the outer tubular member of the cross arm which is to the right of line 75.

The telescopic cross arm structure of Fig. 13 is provided to enable an initial pilot cut to be made adjacent the centre of the coupon which is to be cut from the pipe. It is desirable to be abl e to make a pilot cut so that if an initial cut is made which is t oo deep, resulting in damage to the pipe liner, this will not be a prob-.e:.' providing the initial cut is remote from the perimeter c: the final tu t . Thus the user can make a pilot cut, precisely adjust the position t . the hand wheel 50 (Fig. 11) such that the cut is just sufficient -, - enable removal of the pipe wall without any damage tc the liner. .-.:.:. the hand wheel 73 can then be rotated to return the cross arm to tr.t configuration shown in Fig. 13 before the hand wheel 65 is rotated to cause rotation of the shaft 62. With such an arrangement a user c the illustrated apparatus presented with the task of cutting a coupon from the wall of a pipe of unknown thickness, can use trial and error to determine the wall thickness before moving the cutter to tne appropriate position for coupon removal.