GB2240057A - Device for cutting an aperture in a hollow cylindrical object - Google Patents

Abstract

The device comprises a frame (4, 6), a cutting tool (21) which has a cutter bit (23) and is so mounted on the frame as to be movable relative to the frame, and drive means (12, 28) for moving the cutting tool relative to the frame. The cutting tool (21) is so mounted that a point on the cutter bit (23) is constrained to move in a closed loop which includes circumferential and axial movement so that it lies in a notional cylindrical surface corresponding, in use, to the cylindrical wall of the hollow object, and the drive means (12, 28) is arranged to cause the cutting tool (21) to move round the closed loop so that the cutter bit (23) cuts an aperture in the cylindrical wall of the object. <IMAGE>

Description

Device for cutting an aperture in a hollow cylindrical object.

The present invention relates to a device for cutting an aperture in a hollow cylindrical object.

When plastics water pipes are laid in the ground they are often protected against accidental damage by hollow cylindrical ducting which surrounds the pipe. If it becomes necessary to gain access to the pipe, for example, to make a new connection to the pipe, an aperture must be made in the duct at the desired point.

Previously, ducting for water pipes was made from a hard, brittle material and this enabled an aperture to be made in the ducting simply by hitting the ducting with a hammer. Now, however, flexible ducting made of polyethylene is increasingly being used and, since this material is not brittle and does not break when hit with a hammer, producing an aperture in the ducting without damaging the pipe is much more difficult. Further, since a machine for reliably producing apertures in pipe ducting that is not brittle has not until now been available, it has been necessary for a workman to dig a large hole alongside the pipe, into which hole he has had to climb to cut an aperture manually in the duct. Such a hole must be large enough to accommodate the workman, and it is therefore time-consuming and costly to dig and may cause a great deal of disruption to the immediate environment.

It is an object of the invention to provide a device which mitigates at least some of the above difficulties.

According to the present invention, there is provided a device for cutting an aperture in a hollow cylindrical object, which device comprises a frame, a cutting tool which has a cutter bit and is so mounted on the frame as to be movable relative to the frame, and drive means for moving the cutting tool relative to the frame, the cutting tool is so mounted on the frame that a point on the cutter bit is constrained to lie on a closed loop that lies in a notional cylindrical surface with the axis of the bit extending radially inwards with respect to the notional cylindrical surface so that, when the device is located in an operational position with respect to the hollow cylindrical object, that is a position in which the axis of the notional cylindrical surface coincides with the axis of the hollow oject, the axis of the bit is substantially radial to the longitudinal axis of the object, and a point on the bit remains at a constant distance from the axis of the hollow object, and the drive means is arranged to cause the cutting tool to move round the closed loop so that the cutter bit cuts an aperture in the cylindrical wall of the object.

Use of the device enables an aperture to be cut reliably in a pipe duct without damaging an enclosed pipe, to permit a connection to be made to the pipe.

Because the device may be operated automatically, an aperture can be cut in a buried pipe duct without the need to dig a hole large enough to accommodate a workman.

The device may be lowered down a small hole onto the duct, thereby reducing the disruption to the immediate environment.

Preferably, the cutting tool is so mounted on the frame that the loop is substantially rectangular in projection, the loop comprising two straight sides each substantially parallel to the longitudinal axis of the notional cylindrical surface and two arcuate sides each coinciding substantially with a part of a circumference of the notional cylindrical surface.

Preferably, the device includes a shaft of which the axis extends parallel to the axis of curvture of the notional cylindrical surface and on which there is mounted a member which can move along the shaft and which is arranged to cause the cutting tool to move along a straight side of the loop when the said member moves along the shaft.

Preferably, the shaft is so mounted that it is movable in such a manner that its axis is movable in a second notional cylindrical surface coaxial with the first-mentioned cylindrical surface, the arrangement being such that, when the shaft is caused to move in that manner, the resulting movement of the said member mounted on the shaft causes the said point on the cutter bit to move along an arcuate side portion of the said loop.

Preferably, the shaft has mounted on it at least one gear wheel, not rotatable relative to the shaft, the device includes at least one fixed gear with the or each of which the gear wheel, or one of the gear wheels, is in engagement, the shaft is rotable about its own axis, and the arrangement is such that rotation of the or each gear wheel resulting from rotation of the shaft about its own axis causes the axis of the shaft to move in the second notional cylindrical surface.

Preferably, the shaft is threaded and the member mounted on the shaft is internally threaded for engagement with the thread on the shaft, so that rotation of the member relative to the shaft causes the member to move along the shaft.

Preferably, the arrangement is such that movement along the shaft of the member mounted on the shaft in each direction is limited, so that when the member reaches either of the limiting positions, further rotation of the member causes the shaft to rotate with the member.

Preferably, the drive means is arranged to cause the member mounted on the shaft to rotate about the axis of the shaft, and the drive means is arranged to reverse the direction of drive of the member on the shaft when the torque required to drive the member on the shaft exceeds a predetermined magnitude larger than the torque required to drive the member when it is rotating with the shaft so that when, by reason of the engagement between the gear wheel or gear wheels on the shaft and, the fixed gear or gears, the shaft is brought to a position corresponding to the bringing of the said point on the cutter bit to one end of an arcuate side portion of the closed loop, the direction of drive of the member on the shaft reverses to cause the member to rotate relative to the shaft and so move along the shaft in a direction away from that arcuate side portion of the closed loop.

The drive means is thus arranged to move the cutter bit around the closed loop simply by rotating the member mounted on the shaft first in one direction and then in the other. Only one motor for rotating the member is therefore required. The correct moment for reversing the drive to the rotatable member may be ascertained simply, for example, by sensing the hydraulic pressure of a hydraulic drive motor.

Preferably, the frame includes arcuate guide means for guiding the cutter bit along each of the arcuate sides of the closed loop, the centre of curvature of each of the arcuate guide means lying on the longitudinal axis of the notional cylindrical surface.

The cutting tool may engage the arcuate guide means at two circumferentially-spaced points, to retain the axis of the cutter bit in a substantially radial orientation with respect to the longitudinal axis of an object in the operational position.

The cutting tool may be connected to the arcuate guide means via two shafts which are connected to one another with their axes parallel to, and at a constant separation from, one another.

The arcuate guide means may include at least one arcuate slot, an end or ends of the shaft or shafts being mounted for movement along the slot.

The device may include means for so releasably clamping the frame to a hollow cylindrical object as to maintain the device in the operational position with respect to that object.

The present invention further provides a method of cutting an aperture in a hollow, cylindrical object, in which a device as described above is securely located in the operational position relatively to the object and, with the cutter bit driven, the bit is moved in a closed loop within the cylindrical wall of the object.

A cutting device constructed in accordance with the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a side view partly in section of the cutting device, correctly located in the operating position in relation to a pipe duct to be cut; Fig. 2 is a cross-sectional view on line I-I of Fig. 1; and Figs. 3 and 4 are cross-sectional views of parts of the device on a larger scale than Figs. 1 and 2.

Referring to Figs. 1 and 2 of the accompanying drawings, the cutting device, indicated generally by the reference numeral 1, is shown located in the operating position on a protective duct 2 surrounding a water pipe 3. The device 1 comprises a pair of similar, substantially inverted U-shaped end plates, which are indicated generally by the reference numeral 4, and which are joined to one another at their lower ends by two tie rods 6. The ends of the tie rods 6 are located in holes 7 in the lower ends of the end plates 4, and are secured by screws 8.The end plates 4 and the tie rods 6 form a rigid frame of substantially inverted U-shaped crosssection which, in use, is positioned in the manner of a saddle over the pipe duct 2, the axis of the pipe duct in the operational position being parallel to the axes of the tie rods 6, and perpendicular to the planes of the end plates 4. The frame is clamped to the pipe duct 2 with conventional pipe clamps (not shown in the drawings).

Each of the end plates 4 is provided with an arcuate slot 9 which extends through the thickness of the plate and round a part of its circumference so that it subtends an angle of approximately 2300 at the longitudinal axis of the pipe duct 2, with which the centre of rotation of the arc of the slot coincides in the operational position. An internal gear 10 is provided in a recess 11 on one face of each plate 4, the tips of the gear teeth lying substantially in the radially outer surfaces of the slot 9. The internal gear subtends an angle of approximately 2000 at the longitudinal axis of the pipe duct 2, a portion of one end of the slot 9 not being equipped with gear teeth.

A lead shaft 12, having a spur gear 13 on each end, is located between the end plates 4, its end portions 14 so extending through the slots 9 in the respective end plates 4 that the teeth of the spur gears engage the teeth of the respective internal gears 10. The portions 14 of the lead shaft 12 that are within the slots 9 are journalled in brass bearings 15 which are slidable along the slots. Rotation of the lead shaft causes it to move in an arc around the slots, the axis of the shaft always remaining parallel to the longitudinal axis of the pipe duct 2 in the operational position.

A follower shaft 17 also extends between the end plates 4, its ends being journalled in bearings 18 which are slidable along the slots 9. The follower shaft 17 is not provided with spur gears and so does not engage the internal gears 10. The follower shaft can, however, slide freely around the arcuate slot 9.

The lead shaft 12 and the follower shaft 17 are connected to one another by a follower plate 19. The follower plate 19 is provided with two brass bushes 20, through which the lead shaft 12 and the follower shaft 17 extend. The bushes 20 have a sliding fit with the shafts 12, 17, enabling the follower plate 19 to slide backwards and forwards along the shafts, parallel to the longitudinal axis of the pipe duct 2. The follower plate 19 ensures that the lead shaft 12 and the follower shaft 17 are always parallel to one another and at a constant separation to each other, thus constraining the two shafts to move in unison around the arcuate slots 9.

In order to hold the two shafts 12, 17 even more firmly in a constant positional relationship to each other, two further follower plates (not shown) are provided, adjacent to opposite ends of the shafts.

Securely attached to the follower plate 19 is a cutting tool 21 having an output drive shaft 22 to the end of which is attached a milling cutter 23. The axis of the output drive shaft 22 is arranged to be radial to the longitudinal axis of the pipe duct 2 in the operational position and, because of the engagement via the two shafts 12, 17 of the follower plate 19 with the arcuate slots 9 at two circumferentially spaced points, the radial orientation of the output drive shaft 22 to the pipe duct axis is maintained throughout movement of the cutting tool 21 with the follower plate 19 around the arcuate slots 9. The milling cutter 23 is adjusted to extend radially inwards just far enough to cut through the wall of the duct 2 without touching the enclosed pipe 3.Again, because of the engagement of the follower plate 19 via the shafts 12, 17 with the arcuate slots 9, the tip of the milling cutter 23 is constrained to describe an arc of constant radius about the longitudinal axis of the pipe duct 2 as the follower plate moves around the slots.

The output drive shaft 22 of the cutting tool 21 is driven via a cutter gearbox 24 from a flexible drive shaft (not shown). As shown in Fig. 3, the cutter gearbox 24 includes an input drive shaft 25, for connecting to the flexible drive shaft, which engages the output drive shaft 22 via a pair of bevel gears 26, the axes of the input and output shafts being at right angles to one another. The drive shafts 22, 25 and the gears 26 are mounted in a housing 27 comprising two joined parts 27 and 27b, the part 27a surrounding the input drive shaft 25 being rotatable relative to the part 27k surrounding the output drive shaft 22 about the axis of that shaft.

The rotation of the part 27a to the part 27b enables the gearbox 24 to accommodate movement of the follower plate 19 around the arcuate slots 9 without causing excessive flexing of the flexible drive shaft.

Attached to the cutting tool 21 and the follower plate 19 is a drive gearbox 28 for longitudinal and arcuate movement of the cutting tool 21. As shown in Fig. 4, the drive gearbox 28 includes an input drive shaft 29 for connection to the flexible drive shaft (not shown) having a worm 30 which engages a worm gear 31.

The worm gear 31 is provided with an axial, threaded bore 32 through which the lead shaft 12 extends, the lead shaft 12 being provided with an external screw thread 16 which engages the threaded bore.

When the input drive shaft 29 of the drive gearbox 28 is rotated, the resulting rotation of the worm gear 31 causes the drive gearbox 28 to be drawn along the lead shaft 12 producing longitudinal movement of the cutting tool 21 (that is to say, movement parallel to the longitudinal axis of a pipe duct 2 in the operational position).

The drive gearbox 28 will continue to move along the lead shaft 12 until the worm gear 31 abuts the bearing 15 at the end of the lead shaft, when further rotation of the worm gear relative to the shaft is prevented.

Further rotation of the input drive shaft 29 then causes the lead shaft 12 to rotate with the worm gear 31 and, as a result of the engagement of the spur gears 13 with the internal gears 10, the lead shaft is driven around the arcuate slots 9 in the end plates 4. The cutting tool 21 is therefore caused to move in an arc around the circumference of the pipe duct 2. Arcuate movement of the cutting tool 21 does not take place until the worm gear 31 reaches the end of the lead shaft 12, because much greater frictional forces must be overcome to produce arcuate movement of the cutting tool than to produce longitudinal movement.

When the end of the arcuate slot 9 is reached, further movement of the cutting tool 21 is not possible and rotation of the input drive shaft 29 of the drive gearbox 28 is therefore prevented. The flexible drive shaft for the drive gearbox 28 is driven from a hydraulic motor (not shown), which is stopped when the input drive shaft is prevented from rotating, thus causing an increase in the pressure of the hydraulic fluid. A control device (not shown) which operates in a manner known to those skilled in the art, senses this increase in hydraulic pressure and, in response to it, reverses the direction of rotation of the hydraulic motor. The direction of rotation of the worm gear 31 is therefore reversed, causing the cutting tool to move back along the lead shaft 12 in the opposite direction to its original motion.When the opposite end of the lead shaft 12 is reached, the shaft is again forced to rotate with the worm gear 31, causing arcuate movement of the cutting tool 21 around the slots 9 back to its original position.

The movement of the cutting tool is such that the tip of the milling cutter describes a closed loop that lies in a notional cylindrical surface, the axis of which surface coincides with the axis of the pipe duct 2 when the device is located in the operational position with respect to the duct, the closed loop being substantially rectangular in projection and comprising two straight edges parallel to the longitudinal axis of the duct and two arcuate sides each coinciding substantially with a part of a circumference of the duct.

The process of making a connection to a plastics water pipe 1 provided with a protective duct 2, using the pipe cutter device, is as follows: first, a portion of the buried pipe duct 2 is exposed by digging a small hole of, for example, 18" diameter, down to the duct. The pipe cutter device is then arranged with the cutting tool 21 positioned towards the top of the arcuate slots 9, and is lowered by means of a hoist into the hole above the pipe duct 2. The cutting tool drive motor is then activated and, with the milling cutter 23 turning, the device is lowered onto the pipe duct 2 and is clamped thereto. As the device is clamped to the pipe duct 2 in the operational position, the rotating milling cutter 23 cuts a small hole through the duct.

The drive motor is then activated and, because the worm gear 31 will already be abutting one end of the lead shaft screw 16, the cutting tool 21 moves circumferentially to one end of the arcuate slots 9, cutting a circumferential groove in the pipe duct 2. The drive gearbox 28 then ceases to be driven and the resulting increase in hydraulic pressure is sensed by the control device which immediately reverses the direction of the hydraulic motor. The cutting tool 21 is thereby caused to move along the lead shaft 12 and then around the arcuate slots 9, cutting a groove which extends parallel to the axis of the duct 2 and then around its circumference.When the end of the slot 9 is reached, the direction of drive of the hydraulic drive motor is again reversed, causing the cutting tool 21 to extend the groove back along the length of the duct 2 parallel to its axis and then around the duct's circumference to the starting point of the groove. The complete cutting operation therefore cuts a rectangular window in the duct 2, without damaging the enclosed water pipe 3.

When the cutting operation is complete, the pipe cutting device is unclamped from the duct 2 and is hoisted out of the hole. The cut out portion of the duct is then removed or pushed to one side, and a self-welding pipe joint of known type (called a "fusion saddle") is located through the window in the duct 2 onto the pipe 3, and the connection completed in the normal manner.

The hole is then filled in and finished off, the whole operation having taken place with the minimum of disturbance to the surrounding area.

The cutting device may be useful in other applications: for example, for cutting apertures in ducts surrounding other types of pipes or services, such as gas pipes, electricity supply wires, telephone cables etc., or for cutting holes in the pipes themselves. By altering the length of the lead shaft 12 and the arcuate slots 9 the device may be adjusted to cut apertures of different sizes and shapes.

Claims (15)

Claims:

1. A device for cutting an aperture in a hollow cylindrical object, which device comprises a frame, a cutting tool which has a cutter bit and is so mounted on the frame as to be movable relative to the frame, and drive means for moving the cutting tool relative to the frame, the cutting tool is so mounted on the frame that a point on the cutter bit is constrained to lie on a closed loop that lies in a notional cylindrical surface with the axis of the bit extending radially inwards with respect to the notional cylindrical surface so that, when the device is located in an operational position with respect to the hollow cylindrical object, that is a position in which the axis of the notional cylindrical surface coincides with the axis of the hollow object, the axis of the bit is substantially radial to the longitudinal axis of the object, and a point on the bit remains at a constant distance from the axis of the hollow object, and the drive means is arranged to cause the cutting tool to move round the closed loop so that the cutter bit cuts an aperture in the cylindrical wall of the object.

2. A device as claimed in claim 1, in which the cutting tool is so mounted on the frame that the loop is substantially rectangular in projection, the loop comprising two straight sides each substantially parallel to the longitudinal axis of the notional cylindrical surface and two arcuate sides each coinciding substantially with a part of a circumference of the notional cylindrical surface.

3. A device as claimed in claim 2, which includes a shaft of which the axis extends parallel to the axis of curvature of the notional cylindrical surface and on which there is mounted a member which can move along the shaft and which is arranged to cause the cutting tool to move along a straight side of the loop when the said member moves along the shaft.

4. A device as claimed in claim 3, wherein the shaft is so mounted that it is movable in such a manner that its axis is movable in a second notional cylindrical surface coaxial with the first-mentioned cylindrical surface, the arrangement being such that, when the shaft is caused to move in that manner, the resulting movement of the said member mounted on the shaft causes the said point on the cutter bit to move along an arcuate side portion of the said loop.

5. A device as claimed in claim 4, wherein the shaft has mounted on it at least one gear wheel, not rotatable relative to the shaft, the device includes at least one fixed gear with the or each of which the gear wheel, or one of the gear wheels, is in engagement, the shaft is rotatable about its own axis, and the arrangement is such that rotation of the or each gear wheel resulting from rotation of the shaft about its own axis causes the axis of the shaft to move in the second notional cylindrical surface.

6. A device as claimed in claim 5, wherein the shaft is threaded and the member mounted on the shaft is internally threaded for engagement with the thread on the shaft, so that rotation of the member relative to the shaft causes the member to move along the shaft.

7. A device as claimed in claim 6, wherein the arrangement is such that movement along the shaft of the member mounted on the shaft in each direction is lim;ted, so that when the member reaches either of the limiting positions, further rotation of the member causes the shaft to rotate with the member.

8. A device as claimed in claim 7, wherein the drive means is arranged to cause the member mounted on the shaft to rotate about the axis of the shaft, and the drive means is arranged to reverse the direction of drive of the member on the shaft when the torque required to drive the member on the shaft exceeds a predetermined magnitude larger than the torque required to drive the member when it is rotating with the shaft so that when, by reason of the engagement between the gear wheel or gear wheels on the shaft and, the fixed gear or gears, the shaft is brought to a position corresponding to the bringing of the said point on the cutter bit to one end of an arcuate side portion of the closed loop, the direction of drive of the member on the shaft reverses to cause the member to rotate relative to the shaft and so move along the shaft in a direction away from that arcuate side portion of the closed loop.

9. A device as claimed in any one of claims 2 to 8, wherein the frame includes arcuate guide means for guiding the cutter bit along each of the arcuate sides of the closed loop, the centre of curvature of each of the arcuate guide means lying on the longitudinal axis of the notional cylindrical surface.

10. A device as claimed in claim 9, wherein the cutting tool engages the arcuate guide means at two circumferentially-spaced points, to retain the axis of the cutter bit in a substantially radial orientation with respect to the longitudinal axis of an object in the operational position.

11. A device as claimed in claim 10, wherein the cutting tool is connected to the arcuate guide means via two shafts which are connected to one another with their axes parallel to, and at a constant separation from, one another.

12. A device as claimed in claims 9 to 11, in which the arcuate guide means includes at least one arcuate slot, an end or ends of the shaft or shafts being mounted for movement along the slot.

13. A device as claimed in any one of claims 1 to 12, which includes means for so releasably clamping the frame to a hollow cylindrical object as to maintain the device in the operational position with respect to that object.

14. A device for cutting an aperture in a hollow cylindrical object, the device being substantially as described herein with reference to, and as shown in the accompanying drawings.

15. A method of cutting an aperture in a hollow, cylindrical object, in which a device as claimed in any one of claims 1 to 14 is securely located in the operational position relative to the object and, with the cutter bit driven, the bit is moved in a closed loop within the cylindrical wall of the object.