WO2015059475A1

WO2015059475A1 - Pipe cutting apparatus

Info

Publication number: WO2015059475A1
Application number: PCT/GB2014/053157
Authority: WO
Inventors: Benjamin Roland Walter Fermor Shepherd
Original assignee: Shepherd, Peta Anne
Priority date: 2013-10-24
Filing date: 2014-10-23
Publication date: 2015-04-30
Also published as: GB201318845D0; GB2519565A

Abstract

A pipe cutting apparatus (10), especially for cutting or machining a plastics, resin or soft-metallic pipe (20), comprises a frame (32a, 32b) for receiving the pipe (20) to be cut, and cutting means (100a, 100b) carried by the frame (32a, 32b), the cutting means (100a, 100b) and the pipe (20) being relatively rotatable with respect to each other, e.g. by geared drive means, to perform a cut, wherein the cutting means comprise at least one cutting tool (100a, 100b) and a positioning mechanism for controlling the relative position of the cutting tool(s) (100a, 100b) with respect to the pipe (20), wherein the positioning mechanism comprises: (i) secondary biasing means, e.g. a respective coil compression spring (104a, 104b), attached to a respective cutting tool (100a, 100b); (ii) force transmission means, e.g. interconnected primary and secondary hydraulic cylinder devices (80; 102a, 102b), connected to the secondary biasing means (104a, 104b); and (iii) primary biasing means, e.g. a primary coil compression spring (88), connected to the force transmission means (80; 102a, 102b) and actuatable by an actuation lever (90) to apply or receive force respectively to or from the secondary biasing means (104a, 104b) via the force transmission means (80; 102a, 102b); wherein the actuation lever (90) is selectively actuatable either to cause the primary biasing means (88) to apply biasing force, via the force transmission means (80, 102a, 102b), to the secondary biasing means (104a, 104b) so as to advance the respective cutting tool (100a, 100b) into cutting relationship with the pipe (20), or to enable the primary biasing means (88) to receive biasing force, via the force transmission means (80; 102a, 102b), from the secondary biasing means (102a, 102b) so as to retract the respective cutting tool (100a, 100b) out of cutting relationship with the pipe (20).

Description

PIPE CUTTING APPARATUS

FI ELD OF THE I NVENTION This invention relates to a pipe cutting apparatus, more particularly to a pipe cutting and/or machining apparatus for mounting externally on a pipe and comprising a cutter head which is rotatable about the pipe to impart one or more particular cutting and/or machining operations to the pipe. BACKGROUND OF THE I NVENTION AND PRIOR ART

As used herein, the term "pipe cutting" encompasses not only cutting completely through or partially into (i.e. in the manner of a groove or channel in) a pipe wall, but it also includes pipe machining in which a pipe's wall or surface at an end region (or mouth or lip) thereof is machined by a cutting action so as to modify its shape or appearance.

The prior art has many examples of pipe cutting or machining apparatuses for mounting onto a pipe and which include a cutting head carrying a selected cutting tool for performing a particular desired cutting or machining operation, such as grooving or complete cutting-off. One common such type of apparatus comprises a frame, carrying a cutting tool head, which can be easily and quickly mounted on the pipe, drive means for rotating the cutting tool head around the pipe, and means for advancing or biasing the cutting tool towards the pipe as the tool head is driven therearound. One example of such an apparatus is the portable lathe shown in US patent no. US4543861. Here a tool head, rotatable on a mandrel engageable within a pipe, carries a tool for either a cutting-off or a bevelling operation. Advancement of the tool radially with respect to the pipe is achieved by a mechanism comprising a tool-advancing cam carried on a stationary element of the tool head and which intermittently transmits movement via a one-way clutch to the tool head through a rigid linkage including a feed screw associated with a tool slide. This tool-advancing mechanism is however relatively complex, because of the necessity for the linkage to be of variable length so that it can be adapted to cut the pipe at various angles. Another example of a known pipe cutting or machining apparatus is our own earlier design shown in published International patent application WO2007/052035. In this construction, which makes the job of cutting or machining a pipe quicker and easier for an operator, a two-part hinged holder clamps the pipe externally and a cutting head supported thereon is rotatable around the pipe to perform the cutting operation. The cutting head includes a blade whose advancement radially towards the pipe is governed by an indexing mechanism fixed to the frame and including a snail cam and pawl and ratchet device which incrementally advances the cutting blade radially inwardly towards the pipe's axis in response to completion of each revolution of the cutting head around the pipe.

Whilst the above apparatus of WO2007/052035 is an improvement in certain respects upon other known pipe cutting or machining apparatuses, it still relies on a relatively complex tool advancement mechanism, and one that demands quite high engineering of a relatively large number of interconnected moving parts. By its very nature therefore, the blade advancing mechanism is prone to high levels of wear through normal use, thus reducing its working life, and also to a propensity to damage or malfunction from ingress of dirt and foreign bodies that are frequently typical of environments in which the apparatus is often to be used, e.g. building sites.

Some simpler designs of cutting heads for otherwise similar pipe cutting apparatuses are nevertheless already known, which employ a simpler cutting tool biasing arrangement, rather than an incremental tool-advancing mechanism, in order to maintain the cutting tool in optimum radial positioning with respect to the pipe during a cutting operation. Such tool biasing arrangements generally comprise a biasing means, either in the form of one or more springs or one or more hydraulic or pneumatic cylinder devices, to impart what is generally intended to be a substantially constant pressure of the cutting tool against the pipe during the cutting operation. Examples of such cutting head mechanisms using either springs or hydraulic or pneumatic cylinder biasing arrangements are shown for instance in US patents nos. US3942248, US6095021 and US4084463, and published US patent applications nos. US2006/0260133A1 and US2006/0032351A1.

However, these known designs of cutting head which employ spring- or hydraulic (or pneumatic) cylinder-based biasing arrangements have their own drawbacks and practical limitations. For instance, these known biasing arrangements are generally concerned only with the one-way biasing of the cutting tool towards the pipe during a cutting operation, and no regard is given to the issue of how to efficiently withdraw the cutting tool from its cutting position against the pipe as orwhen that may be required (in particularwhen it is required to remove the pipe from the frame), except by resorting to opening up the frame and completely releasing the cutting head from its engagement with the pipe. This of course is time-consuming, leads to greater risk of ingress of dirt or foreign particles that could damage the cutting mechanism, and it makes it difficult or virtually impossible to reassemble the apparatus onto the pipe accurately in order to resume a particular cutting operation at a specific location on the pipe that may be only partially complete.

Furthermore, even though a major aim in many of these disclosed tool biasing arrangements has been to provide a substantially constant pressure (i.e. biasing force) of the cutting tool against the pipe during the cutting operation, this at best only applies to relatively short radial distances of travel of the tool during a given cutting operation. This may hinder the attainment of consistent and accurate cutting operations on pipes with particularly thick walls or over relatively large radial distances, such as certain machining operations e.g. at a pipe's open end.

It is therefore a primary object of the present invention to solve or ameliorate at least some of the above problems associated with prior art pipe cutting or machining apparatuses, by providing an apparatus of the above-defined type but which employs a cutting tool positioning mechanism that is simple and efficient in construction and operation, and also allows for reversible advancement, with improved constancy of pressure over given radial distances, and/or retraction of a cutting tool with respect to a pipe being cut or machined whilst the frame of the apparatus carrying the cutting head remains in situ.

SUMMARY OF THE INVENTION

Accordingly, in a first aspect the present invention provides a pipe cutting apparatus comprising a frame for receiving a pipe to be cut, and cutting means carried by the frame, the cutting means and the pipe being relatively rotatable with respect to each other to perform a cut, wherein the cutting means comprises at least one cutting tool and a positioning mechanism for controlling the relative position of the cutting tool with respect to the pipe,

wherein the positioning mechanism comprises:

(i) secondary biasing means attached to the cutting tool;

(ii) force transmission means connected to the secondary biasing means; and

(iii) primary biasing means connected to the force transmission means and actuatable by actuation means to apply or receive force respectively to or from the secondary biasing means via the force transmission means;

wherein the actuation means is selectively actuatable either to cause the primary biasing means to apply biasing force, via the force transmission means, to the secondary biasing means so as to advance the cutting tool into cutting relationship with the pipe, or to enable the primary biasing means to receive biasing force, via the force transmission means, from the secondary biasing means so as to retract the cutting tool out of cutting relationship with the pipe. In accordance with the invention therefore, the positioning mechanism for the cutting tool is in effect a "push-pull" combination biasing mechanism, in which the primary and secondary biasing means, linked by the interposed force transmission means, act in concert and in reaction to each other's individual biasing force, initiated in a selected direction by the actuation means, to either advance the cutting tool into its cutting engagement position with respect to the pipe, or retract it therefrom.

In certain embodiments of the invention there may be provided a single cutting tool, in which case a single secondary biasing means is also provided attached thereto and actuatable by the primary biasing means via the force transmission means. In other, possibly more preferred, practical embodiments, there may be provided a plurality of (e.g. two or more) cutting tools, each associated with a respective one of a corresponding plurality of secondary biasing means, the plurality of secondary biasing means being actuatable preferably collectively (especially in tandem or in parallel or simultaneously) by the primary biasing means via the force transmission means. Such embodiments comprising a plurality of cutting tools and a plurality of secondary biasing means will be further defined hereinbelow.

In preferred embodiments of the invention, the primary biasing means preferably comprises at least one resilient member, in particular preferably at least one spring, especially at least one compression spring, such as a compression coil spring.

Preferably the secondary biasing means, which is attached (directly or indirectly) to the cutting tool, comprises at least one resilient member, in particular preferably at least one spring, especially at least one compression spring, such as a compression coil spring.

In preferred embodiments of the invention the force transmission means, which preferably is disposed between the primary and secondary springs or other biasing means in order to transmit biasing force from one of them to the other thereof, comprises a hydraulic device. Preferably the hydraulic device comprises a primary hydraulic cylinder associated with, i.e. preferably connected to, the primary biasing means and a secondary hydraulic cylinder associated with, i.e. preferably connected to, the secondary biasing means and in fluid communication with the primary hydraulic cylinder.

In preferred practical forms of such a hydraulic device, the primary hydraulic cylinder contains a hydraulic fluid and a primary piston arranged to receive biasing force from, or transmit biasing force to, as the case may be, the primary biasing means, and the secondary hydraulic cylinder in fluid communication with the primary hydraulic cylinder contains a secondary piston arranged to transmit biasing force to, or receive biasing force from, as the case may be, the secondary biasing means.

In practical examples of such preferred forms of hydraulic device, the primary biasing means (e.g. the primary compression spring) may be mounted within the primary hydraulic cylinder, preferably between an end wall of the cylinder and the primary piston which contacts and acts upon (or reacts to) the hydraulic fluid in the primary hydraulic cylinder. Likewise, the secondary biasing means (e.g. the secondary compression spring) may be mounted within the secondary hydraulic cylinder, preferably between an end wall thereof and the secondary piston which contacts and reacts to (or acts upon) the hydraulic fluid in the secondary hydraulic cylinder.

Preferably the primary and secondary hydraulic cylinders are in hydraulic fluid communication with each other by means of a conduit, e.g. a pipe or tube, which connects them together. Specific components and configurations for such a practical arrangement are well-known in the art of hydraulics in a wide variety of engineering applications.

In preferred embodiments the actuation means of the positioning mechanism comprises a manually operable device, such a pivotable lever, which is selectively configurable into either an advanced position, in which the primary biasing means is caused to impart biasing force in a forward direction, via the force transmission means, to the (or each, in embodiments where there are plural) secondary biasing means and thus to the cutting tool(s) to move it/them into its/their cutting relationship with respect to a pipe mounted in the frame, or alternatively a withdrawn position, in which the (or each) secondary biasing means is permitted to impart biasing force in a reverse direction, via the force transmission means, to the primary biasing means and thus to retract the (or each) cutting tool from its cutting relationship with respect to the pipe.

The preferred action of this combined "push-pull" biasing arrangement between its advanced and withdrawn position is thus preferably instigated by manual pivoting of the preferred actuation lever between respective "down" and "up" stop limiting positions. In particularly preferred examples of such a pivotable actuation lever, the lever includes a detent device for locking it into at least its advanced position (i.e. "down", corresponding to the cutting tool cutting position). The detent device may conveniently be constituted by a detent portion of the lever itself. A corresponding detent device may of course be provided, if desired, for locking the actuation lever into its withdrawn position (i.e. "up", corresponding to the cutting tool retracted position).

In practical embodiments of the invention, the pipe cutting apparatus may be designed such that the cutting means comprises any desired number of cutting tools, for example one or two, or possibly three or more, cutting tools. In the case of a plurality of cutting tools, each cutting tool may preferably have a different construction or configuration from the other(s), such that each cutting tool is designed to perform a specific cutting or machining operation different from the other(s). For example, there may be provided two distinct cutting tools, preferably axially spaced from one another (i.e. longitudinally with respect to the pipe to be cut), a first one configured and positioned for complete transverse cutting through of the wall of the pipe to be mounted in the frame, and a second one configured and positioned for cutting an annular groove or channel in the pipe outer wall a short distance from the resulting cut pipe (cut by the first cutting tool). Such a dual cutting operation may frequently be required when preparing cut pipe ends for subsequent interconnection to other components of an overall pipeline arrangement, and the ability to carry out both cutting operations simultaneously is particularly advantageous in terms of time, cost and operator resources.

It is of course within the scope of the invention to utilise any number or combination of different cutting tools, each associated with its own secondary biasing means. In addition to tools for complete transverse cutting-through of a pipe wall or machining such as grooving (as mentioned above), alternative cutting tools which may be employed in apparatuses of the invention may include: that for removing one or more outer layers of the pipe wall (such as a plastics coating from a resin pipe) to allow the pipe to be joined to another e.g. by butt-fusion; that for removal of irregularities from the outer surface of the pipe, e.g. for providing a cut end of the pipe with a clean, smooth outer surface of substantially uniform diameter to allow the pipe to be joined to another e.g. by electro- fusion; that for bevelling or chamfering of the edge(s) of a cut pipe end, e.g. at an acute or an obtuse angle with respect to the pipe's longitudinal axis; or that for some other alteration or modification of the shape or profile of an already cut end, end portion, mouth or lip of the pipe. Practical examples of cutting tools suitable for any of the above jobs are readily available in the technical and trade literature.

Thus, and in embodiments of the invention which employ such a plurality of cutting tools, the said positioning mechanism preferably acts upon and is constructed and configured to control the position of all the cutting tools simultaneously. In such embodiments the positioning mechanism therefore preferably comprises:

(i) a plurality of secondary biasing means each attached to a respective one of the plurality of cutting tools;

(ii) force transmission means connected to each of the secondary biasing means; and

(iii) primary biasing means connected to the force transmission means and actuatable by actuation means to apply or receive force respectively to or from each of the secondary biasing means via the force transmission means;

wherein the actuation means is selectively actuatable either to cause the primary biasing means to apply biasing force, via the force transmission means, to each of the secondary biasing means so as to advance each of the cutting tools into its respective cutting relationship with the pipe, or to enable the primary biasing means to receive biasing force, via the force transmission means, from each of the secondary biasing means so as to retract each of the cutting tools out of its respective cutting relationship with the pipe.

When applied to such embodiments employing plural cutting tools each with its own respective secondary biasing means, the above-defined preferred force transmission means may comprise the above-defined primary hydraulic cylinder associated with, i.e. preferably connected to, the primary biasing means, and a plurality of secondary hydraulic cylinders each associated with, i.e. preferably connected to, a respective one of the secondary biasing means (each connected to its own cutting tool), with each of the secondary hydraulic cylinders being connected, preferably in parallel or tandem with the other(s) secondary hydraulic cylinder(s), in fluid communication with the primary hydraulic cylinder. In this way the single primary hydraulic cylinder may be coupled with each of the secondary hydraulic cylinders collectively, and thus actuation of the primary hydraulic cylinder by the actuation lever (or other actuation means) may act upon all the secondary hydraulic cylinders, and thus all the cutting tools, simultaneously. In practical embodiments of the invention the apparatus preferably further comprises drive means for rotating the cutting means and the frame relative to each other. Preferably the cutting means is carried on a rotatable tool carrier in the form of a circular or annular ring mounted on an axially oriented circular rotational bearing arranged within the frame, and the tool carrier and frame are rotatable with respect to each other by the drive means. The cutting means, including the one or more cutting tools and the associated positioning mechanism, may conveniently be located in a forward section of the rotatable tool carrier ring. The rotatable tool carrier ring may for example be contained within an annular channel (or cavity) machined or moulded into the frame. Preferably the drive means is mounted on the frame and acts on the tool carrier to rotate it within the (preferred) annular channel in the frame about its (preferred) axially-oriented bearing and circumferentially with respect to the pipe. The drive means preferably incorporates a gear mechanism, in order to permit or achieve suitable rotational speeds of the cutter head assembly around the pipe during a cutting operation. The drive means may be manually powered or powered by an external power source, e.g. electric. An example of a suitable electrically powered drive means is an electric power drill.

In preferred embodiments of the apparatus according to the invention, the frame may comprise a pair of articulated frame sections hinged with respect to each other to permit a pipe to be inserted therebetween and the frame sections closed around the pipe to clamp it therebetween. Preferably each frame section is a semi-annular or semi- cylindrical frame section (i.e. a half-shell), the two frame sections preferably being symmetrical. Preferably the frame includes at least one locking means for locking the frame sections in their closed, clamping configuration. Preferably a pair of such locking means are provided, spaced apart on the frame in an axial direction with respect to the pipe. The or each locking means is preferably an over-centre locking clamp device, examples of which are well-known in the art. In many preferred embodiments of the apparatus according to the invention, the frame may include adjustable gripping means, preferably radially adjustable gripping means, for altering the effective internal diameter of the space between the frame sections, in order that the frame may accommodate and securely clamp pipes of various different diameters.

In particularly preferred practical embodiments of the apparatus according to the invention, the frame preferably comprises a first (rearward) frame part for primarily supporting and clamping the pipe at a first axial location thereon, and if provided, the aforementioned adjustable gripping means are provided in or on said first (rearward) frame part, and a second (forward) frame part axially spaced from the first (rearward) frame part, on which is provided or mounted the tool carrier carrying the cutting means (comprising the one or more cutting tools and its/their associated positioning mechanism). The first (rearward) and second (forward) frame parts may be integrally formed as a single, unitary frame body, or alternatively may be joined or united together by suitable fixing means, such as by one or more, preferably a plurality of (especially a plurality of equi-angularly disposed), axially extending parallel connecting members, struts, rods or arms.

In practical embodiments of the apparatus according to the invention, and particularly in cases where the one or more cutting tools is/are mounted in one circumferential region of the tool carrier that revolves with respect to the frame, it is preferred that at least one counter-support device (or a respective one of a plurality of counter-support devices, in the case of a plurality of cutting tools) is/are provided on the tool carrier substantially diametrically opposite to the or the respective cutting tool(s). This serves to counter the radially inward cutting forces exerted by the cutting tool(s) as it/they is/are forced into its/their cutting relationship with a pipe mounted in the frame during a cutting operation.

The general structural frame parts of the apparatus of the invention may conveniently be made from any suitable strong, rigid material, for example cast or moulded metal. Alternatively, suitably tough and rigid plastics material may be used. In preferred embodiments of the invention, the one or more cutting tools are movable and thus positionable by the positioning means preferably in a given range of radial distance travel with respect to the pipe. The maximum and minimum limits of the radial distance of travel will in practice preferably be defined by the respective physical dimensions and resilience properties of the primary and secondary biasing means, e.g. springs, and also to some extent preferably the dimensions and configuration of the primary and secondary hydraulic cylinders (or other force transmission means) which link them together. A particular practical set-up of the components of the positioning mechanism may thus dictate a given practical distance of radial travel of the cutting tool(s) that is possible or permitted for that set-up. Because of the dual springs (or other biasing means) arrangement effectively in series with one other, instead of a single biasing means as in the case of prior art cutting tool biasing arrangements, it may be expected that a greater degree of constancy, i.e. less variability in, biasing force of the cutting tool(s) radially against the pipe is achievable over a given distance of radial travel of the cutting tool(s) than has hitherto been possible. This may serve to improve the consistency and accuracy of cutting operations on pipes with particularly thick walls or over relatively large radial distances.

In order to further enhance the utility of apparatuses according to the present invention, it may be provided that the cutting means, comprising the cutting tool(s) and its/their positioning mechanism, are locatable on or in the frame in any one of a plurality of radial positions or locations with respect to a pipe to be mounted within the frame, each said radial position corresponding to, and providing for, a respective different range of radial distance of travel of the cutting tool(s). The range of distance travel provided or permitted by any one defined radial position may overlap to some extent with the range of distance travel provided or permitted by one or more of the other defined radial positions. For provision of such plural radial positions of the cutting means on or in the frame, the frame may preferably comprise a plurality of mounting means, each at a different radial pitch, onto (or into engagement with) any one of which the cutting means may be mounted to provide for a specific defined maximum and minimum radial position, and thus distance of radial travel, with respect to the pipe to be mounted within the frame.

Suitable such plural mounting means may preferably comprise a plurality of mounting formations, e.g. lugs, pins, dovetail protrusions or recesses, spaced radially on at least one of the frame, e.g. forward part of the frame, and the cutting means, with at least one corresponding, preferably complementary, mounting formation provided on the other of the frame and the cutting means. By appropriate selection of the mutually engageable mounting means with which the cutting means are thus mounted on the frame, a desired given general radial positioning of the cutting tool(s) can be provided, thus defining the permitted range of radial distance of travel between maximum and minimum radial positions with respect to the frame that the cutting tool(s) can move therewithin, as further defined by the maximum and minimum limits of travel of the primary and secondary biasing means of the positioning mechanism.

To facilitate quick and easy moving of the cutting means between different defined radial mounting positions or locations, the cutting means may conveniently be carried on a mounting plate and the mounting plate attached to the frame via a suitable blanking plate, which blanking plate is preferably either moveable or interchangeable with one or more other blanking plates. The blanking plate is preferably a selected one of a plurality of differently constructed and/or configured blanking plates that each define, by virtue of its own unique arrangement of plural mounting formations, a unique radial position/location with respect to the frame. Thus, one or more such blanking plates, each constructed and/or configured with an appropriate (and preferably unique) arrangement or array of mounting formations (especially such formations of which at least some are complementary to corresponding mounting formations on the cutting means' mounting plate and/or the frame), may be provided for use with the apparatus, e.g. as a spare part or part of an overall kit of parts or components for use with a particular apparatus. Thus, in use, with the cutting means' mounting plate attached to the frame via a particular selected blanking plate (which allows for a specific defined range of radial distance travel of the cutting means unique to that blanking plate), if or when it is desired to change the range of radial distance travel of the cutting means, it is simply a matter of detaching the cutting means (carried on its mounting plate) from the existing blanking plate, replacing that blanking plate with another, different, blanking plate with a different arrangement of mounting formations, and then re-attaching the cutting means (carried on its mounting plate) onto the new blanking plate, whereby the new blanking plate defines the new radial position/location of the cutting means and thus its new range of radial distance travel. Practical examples of this overall mounting mechanism, and suitable mechanical arrangements by which the cutting tool is radially moveable (towards and away from the pipe) through its cutting distance of travel yet replaceably mounted onto the frame in a desired radial position/location by use of such mechanism(s), will be described hereinbelow in the context of an especially preferred practical embodiment discussed in conjunction with drawings.

In order to yet further enhance the utility of apparatuses according to the present invention, it may be provided that the cutting means, comprising the cutting tool(s) and its/their positioning mechanism, or preferably at least one of the cutting tools of the cutting means (with its respective secondary biasing means) in cases where a plurality of cutting tools (and associated secondary biasing means) are provided, are mounted with respect to the frame in an axially (i.e. longitudinally) variable and/or adjustable position. This may be for example in a corresponding manner to the means of adjustment of a tool position in a conventional lathe. For this purpose the frame may comprise axially moveable and/or adjustable mounting means which carry the cutting means (or individual cutting tools each with its respective secondary biasing means), which mounting means preferably include clamping means for locking the cutting means (or respective cutting tool) in a desired axial position with respect to the frame once it has been moved to its desired axial location.

Such axially moveable/adjustable mounting means may for example include one or more mounting rods, bolts, screw-threaded members, pins, or any of the aforesaid, upon which the cutting means (or cutting tool(s)) are carried and are slidable along, together with clamping means such as suitable nut(s), clip(s) or other clamping or locking device(s), examples of which are well known in the engineering art.

The present invention is applicable to the cutting or machining of pipes made from a variety of materials, such as are commonly used in various practical applications for the transport of fluids such as liquids (e.g. water) or gases. Pipes made of plastics or resin material (e.g. PVC or uPVC) are an especially preferred application of the invention. This is primarily due to the relatively low hardness of such materials, which may be preferred over much harder materials such as (many) metals and ceramics, where a considerably greater radial cutting force may be required to accomplish a required cut than is possible with some embodiments of the apparatus of this invention, particularly those which employ springs (or other primary and secondary biasing means) which are able only to impart relatively low biasing forces. However, the invention may still find use in the cutting or machining of pipes of certain metals or metal alloys, in addition to plastics materials, if their hardness is suitably low such as to permit efficient accomplishment of a cut by the cutting tool(s) under the achievable combined radial biasing forces of the primary and secondary biasing means of the positioning mechanism.

According to a second aspect of the present invention, there is provided, in combination, a pipe cutting apparatus according to the first aspect of the invention together with a pipe to be cut or machined, the pipe being mounted within the frame of the apparatus. The pipe is preferably clamped in position within the frame by any of the above-defined preferred clamping and/or positioning means. According to a third aspect of the present invention, there is provided a method of cutting or machining a pipe, especially a pipe of plastics or resin material, comprising:

(i) placing the pipe to be cut within the frame of an apparatus according to the first aspect of the invention;

(ii) actuating the actuation means of the positioning mechanism to cause the primary biasing means to apply biasing force, via the force transmission means, to the secondary biasing means attached to the cutting tool, whereby the cutting tool is advanced into cutting relationship with the pipe; and (iii) rotating the cutting means with respect to the pipe while the cutting means is biased into its cutting relationship with the pipe under the combined biasing forces of the primary and secondary biasing means. Once the cutting or machining operation is complete, or when it is desired for any reason to interrupt or temporarily suspend or halt the cutting or machining operation, the cutting tool means may be retracted from its cutting relationship with the pipe by reverse actuation of the actuation means, that is to say, by de-actuating (i.e. releasing) the actuation means to cause the primary biasing means to receive biasing force in a reverse direction, via the force transmission means, from the secondary biasing means attached to the cutting tool (i.e. to cause the secondary biasing means attached to the cutting tool to apply biasing force in a reverse direction, via the force transmission means, to the primary biasing means), whereby the cutting tool is retracted from its cutting relationship with the pipe.

By application of this selectable "push-pull" biasing arrangement, the advancement or retraction in a radial direction of the cutting tool(s) i.e. between its cutting and non-cutting limiting positions with respect to the pipe, may thus be readily achieved and controlled, simply by selective actuation or de-actuation of the actuation means, e.g. pivotable actuation lever. This is achievable, in accordance with the invention, by the pipe preferably remaining in situ within the frame and without requiring the frame to be opened up to release the cutting means from its cutting engagement with the pipe.

Of course however, when it comes to releasing the pipe from the apparatus upon completion of a cutting or machining operation, as with known pipe cutting apparatuses the complete preferred frame assembly can simply be opened up to release the pipe, e.g. by first releasing the preferred over-centre locking clamp(s) and then by swinging the preferred top half of the frame up and clear of the pipe, thus allowing the pipe to be lifted out or the apparatus to be swung clear of the pipe.

Within the scope of this application it is envisaged that the various aspects, embodiments, examples and alternatives, and in particular the individual features thereof, set out in the preceding paragraphs, in the claims and/or in the following description and drawings, may be taken independently or in any combination. For example, features defined or described in connection with one aspect and/or embodiment are applicable to all embodiments, unless expressly stated otherwise or such features are incompatible. BRIEF DESCRIPTION OF THE DRAWINGS

One or more preferred embodiments of the present invention in its various aspects will now be described in detail, by way of schematic example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic axial cross-sectional view of the pipe cutting apparatus of a preferred embodiment;

Figure 2 is a rear end-on view (from the left side as shown in Figure 1) of the apparatus of the preferred embodiment of Figure 1 ;

Figure 3 is a front end-on view (from the right side as shown in Figure 1) of the apparatus of the preferred embodiment of Figure 1 ;

Figures 4(a) and 4(b) are enlarged cross-sectional views of the actuation lever and primary biasing means (only) of the cutting means positioning mechanism of the apparatus of Figure 1 , showing these components in, respectively, a retracted (Fig. 4(a)) and an advanced (Fig. 4(b)) position corresponding to, respectively, non-cutting and cutting positions of the cutting tool(s) with respect to a pipe mounted in the apparatus;

Figure 5 is an enlarged schematic cross-sectional view on arrows V-V in Figure 1 , of part of the cutting head arrangement of the apparatus of Figure 1 , showing a first radial mounting position of the cutting means relative to the frame, using a first species of blanking plate, which provides for a first range of radial distance travel of the cutting means upon actuation and release of the actuation lever of the positioning mechanism;

Figure 6 is an enlarged schematic cross-sectional view, corresponding to that of Figure 5, of the same part of the cutting head arrangement of the apparatus of Figure 1 , but showing a second radial mounting position of the cutting means relative to the frame, using a second species of blanking plate, which provides for a second range of radial distance travel of the cutting means upon actuation and release of the actuation lever of the positioning mechanism;

Figure 7(a) is a schematic part-cross-sectional view of the same general part of the cutting head arrangement of the apparatus of Figure 1 as shown in Figure 5, but shown without the cutting means for clarity, illustrating schematically a preferred axial adjustment mechanism by which the axial positioning of the cutting means relative to a pipe mounted in the frame may be selectively adjusted; and

Figure 7(b) is a schematic left side view of Figure 7(a), further illustrating schematically the preferred axial adjustment mechanism.

DETAILED DESCRIPTON OF EMBODIMENTS Referring firstly to Figure 1 , the preferred pipe cutting and/or machining apparatus, shown generally as 10, is mountable on or around a pipe 20, such as a plastics (e.g. PVC) water supply pipe, by means of mutually pivotable upper 32a and lower 32b semi- cylindrical or half-shell frame sections. The upper and lower frame sections 32a, 32b are pivotally hinged together by a known hinging arrangement, such as via hinge rod 134. By way of example, the diameter of the pipe 20 may be typical of standardised pipe sizes in the water or gas industries, e.g. anywhere from about 150 mm up to about 255 mm in diameter.

In order accurately to centre and locate the pipe 20 concentrically within the frame 32a, 32b, the rearward (i.e. left-hand, as shown in Figure 1) section of the frame is provided with a centring mechanism comprising a series, e.g. an arcuate array, of preferably equi- spaced (or equi-angularly disposed) grippers 34 (as shown in further detail in Figure 2) which resiliently bear against the outer wall of the pipe 20 and self-centre it within the frame. As shown in Figure 2, each gripper 34 comprises a lug 36, e.g. of hardened steel, spring-mounted within a respective recess or hole formed in the frame by means of a respective coil compression spring 38. Each respective mounting spring 38 bears at its radially outermost end against a respective rotatable cam 39 mounted on the frame via a pivot pin or bolt 33, such that each gripper 34 is independently slidable within its recess or hole so as to bear against, under the biasing force of its respective spring mounting 38, the outer wall of the pipe at its own circumferential location and to take up any variations in the outer radius of the pipe, whereby the pipe 20 is held stably and concentrically within the frame by the grippers 34 collectively. The pivot pins or bolts 33 may for instance be adjustable into, and/or securable in, any given optimum orientation by means e.g. of an alien key, spanner, screwdriver or other suitable and appropriate adjustment tool.

Although not shown in Figure 1 , once the pipe 20 has been positioned within the frame 32a, 32b, in practice the upper and lower frame sections may be secured together, in order to assist the stable and secure clamping of the pipe within the frame, by means of at least one, preferably a pair of, clamping locking devices, e.g. a pair of over-centre locking clamps, one axially spaced from the other. Examples of such locking clamps are well known in the art.

Formed (e.g. by integral moulding or casting or post- manufacture machining) in a forward (i.e. right-hand, as shown in Figure 1) section of the frame 32a, 32b is a part-cylindrical, part-annular channel or cavity 50 in which is mounted via a rotational bearing (not explicitly shown) a generally cylindrical tool carrier ring 40a, 40b. A forward section 30a, 30b of the tool carrier ring 40a, 40b carries and has mounted thereon the cutting means which constitutes the cutting head, comprising the one or more cutting tools 100a, 100b and the associated tool positioning mechanism (the components and operation of which are described further below).

Mounted atop the frame section 32a is the drive means by which the tool carrier ring 40a, 40b is drivable around and relative to the frame, i.e. relative also to the pipe 20. The drive means comprises a drivable drive shaft 70 (rotatable such as by arrow 72), which has a forward end portion (not shown) which meshes with a toothed gear wheel 60 which drives a correspondingly toothed radially outermost portion 40c of the carrier ring 40a, 40b. The drive shaft 70 is drivable from outside the apparatus by an external power source, which could be manual but more preferably is an electric motor, e.g. an electric power drill.

Turning to Figure 3 in combination with Figure 1 , the forward section 30a, 30b of the tool carrier ring 40a, 40b carries and has mounted thereon the cutting head, comprising one or more cutting tools 100a, 100b. The two cutting tools 100a, 100b are spaced apart axially (i.e. longitudinally with respect to the pipe) from each other by a suitable distance (see below) and also preferably spaced apart circumferentially a short distance on the tool carrier ring but in the same general region or sector thereof. Mounted in or on the tool carrier ring, substantially diametrically opposite (i.e. at approximately 180 degrees relative to) each respective cutting tool 100a, 100b, is a respective counter-support device 120, 130. Each such counter-support device comprises a pair of (preferably) rotatable (e.g. about a respective pivot pin) support lugs or wheels 120 (which optionally may be contained within a cup or armature, as shown in Figure 1) for abutting or bearing against the outer wall of the pipe 20 during its cutting and which are spring-mounted by coil compression springs 130 in a recess in the forward section 30b of the carrier ring 40a, 40b. Thus, each respective counter-support device 120, 130 serves to support the pipe diametrically opposite to each respective cutting tool 100a, 100 during its cutting operation, and thus preferably also to absorb excess radial forces on the pipe that may otherwise tend to displace or distort it. In the illustrated embodiment being described here, the apparatus comprises two cutting tools 100a, 100b, each of a different form and construction, such that each tool is designed and intended to do its own unique cutting and/or machining job on the pipe that is to be mounted within the apparatus. In this particular example, the rearward (i.e. left- hand) cutting tool 100a may for instance be designed to cut merely an annular, or semicircular-sectioned or other shaped, groove or channel in the outer wall of the pipe 20 part-way only through its thickness, whereas the forward (i.e. right-hand) cutting tool 100b may for instance be designed to perform a clean cutting-off of the pipe 20 completely through its full wall thickness whilst simultaneously forming a bevelled edged on the open cut pipe end. This combined arrangement of cuts utilising two distinct cutting tools - as well as the axial (i.e. longitudinal) spacing of the two tools - may for instance be particularly useful in the cutting of plastics pipes for subsequent interconnection in a known manner in the construction of a typical water or gas pipeline. Other types, designs, numbers and combinations of cutting tools may of course be possible.

Turning now to the cutting tools' positioning mechanism, referring in particular now to Figures 1 , 3, 4(a) and (b), the principal components of the positioning mechanism are primary hydraulic cylinder 80, respective secondary hydraulic cylinders 102a, 102b each associated and connected to one of the respective cutting tools 100a, 100b, and actuation lever 90. The primary hydraulic cylinder 80 houses a primary piston 85 connected to a primary piston rod 84, and a primary compression coil spring 88 mounted behind the head of the primary piston 85. Forward of the primary piston head, within the primary cylinder 80, is located a volume of a hydraulic fluid 89, such as a hydraulic oil. Practical examples of suitable hydraulic oils or other fluids are well-known in the art of hydraulics in a wide variety of engineering applications.

Each secondary hydraulic cylinder 102a, 102b, is constructed correspondingly to the primary hydraulic cylinder: Each secondary hydraulic cylinder 102a, 102b houses a secondary piston (not explicitly labelled in Figure 1 for clarity) connected to its own secondary piston rod which is attached to its respective cutting tool, and a respective secondary compression coil spring 104a, 104b is mounted behind the head of the respective secondary piston. Again, forward of each respective secondary piston head is located hydraulic fluid, which is in fluid communication with the hydraulic fluid 89 in the primary hydraulic cylinder 80 via connecting tubes or conduits 86a, 86b. Thus, hydraulic fluid 89 may pass back and forth between the primary and each respective secondary hydraulic cylinder 102a, 102b as the primary and secondary pistons are forced back and forth under the biasing action of the respective primary 88 and secondary 104a, 104b coil compression springs.

As will be appreciated, when the primary piston rod 84 is forced into the primary hydraulic cylinder 80, the primary coil compression spring 88 undergoes compression and applies a biasing force to the primary piston 85 to force hydraulic fluid 89 out of the primary cylinder, through interconnection tubes 86a, 86b into each respective secondary hydraulic cylinder 102a, 102b. This causes each respective secondary coil compression spring 104a. 104b to react, become compressed, and thus to exert a corresponding biasing force of its own onto its attached cutting tool, thereby forcing the tool radially inwardly relative to the pipe and thus urging it into a cutting position against, e.g. into the wall of, the pipe. This forcing of the primary piston 85 into the primary hydraulic cylinder 80 is accomplished by pivoting, such as by manual manipulation by an operator, of the actuation lever 90 from a "withdrawn" position - as shown in Figure 4(a) - into an "advanced" position - as shown in Figure 4(b). The actuation lever 90 is pivoted e.g. about a pivot pin 96 mounted on the carrier ring. In practice the lever 90 is preferably shaped with an arcuate, curved or cam bearing surface or face 94, against which the distal end of the primary piston rod 84 abuts, so that the rod 84 is forced along the primary cylinder as the lever 90 is pivoted about its pivotal bearing 96.

Conveniently, and preferably, the bearing face or surface 94 of the actuation lever 90 terminates in a detent portion 98, behind which the distal end of the primary piston rod 84 becomes trapped once the lever is pivoted to the end of its pivotal travel, whereby the lever is effectively detained in that position.

In the "withdrawn" pivotal position of the actuation lever 90 - as shown in Figure 4(a) - the primary compression spring 88 may preferably be in its relaxed, unbiased configuration, as also are each of the secondary compression springs 104a, 104b in the secondary hydraulic cylinders. In this configuration the total volume of hydraulic fluid 96 in the primary and secondary hydraulic cylinders and the interconnection tubes 86a, 86b preferably is at a maximum and substantially fills the free volume of these components so as to provide a maximum available transmission of biasing force once the actuation lever 90 has been pivoted into its maximum, "advanced" position - as shown in Figure 4(b).

When it is desired to retract the cutting tools 100a, 100b from their cutting positions relative to the pipe, it is straightforward to do this while the pipe remains in situ, i.e. without having to resort to disconnecting the frame parts and completely releasing the pipe from within the frame in order to release the cutting tools from their cutting positions. This retraction of the cutting tools is achieved, in accordance with the invention as exemplified by this embodiment, by simply pivoting the actuation lever 90 in the reverse direction, i.e. from its "advanced" position - as shown in Figure 4(b) - back to its "withdrawn" position - as shown in Figure 4(a). This release of biasing force from the (now relaxed) primary coil compression spring 88 in the primary hydraulic cylinder 80 allows the respective secondary coil compression springs 104a, 104b - which are under compression - in the respective secondary hydraulic cylinders (attached to the respective cutting tools) to prevail and themselves now to exert a reverse biasing force in the opposite direction from before The effect of this is to force hydraulic fluid 89 back from the secondary hydraulic cylinders 102a, 102b through the interconnecting tubes 86a, 86b and back into the primary hydraulic cylinder 80, thereby causing the primary piston 85 to retract under the force of the incoming hydraulic fluid and as permitted by the now relaxed primary coil compression spring 88. In this manner, what was previously a "push" action upon the secondary compression springs in reaction to a forward (i.e. "advancing") force exerted by the actuation lever via the primary compression spring now becomes a "pull" action in the reverse (i.e. "retracting") direction. Thus, by reverse pivoting of the actuation lever 90 back into its "withdrawn" position, the secondary compression springs 104a, 104b are permitted to pull their respective cutting tools 100a, 100b into retraction from their cutting position relative to the pipe. In this way, the dual (primary and secondary) compression springs arrangement coupled by the dual (primary and secondary) hydraulic cylinder devices constitute a reversible indirect force transmission arrangement between the actuation lever 90 and the cutting tools 100a, 100b. This makes for a much more efficient, accurate and mechanically simplified arrangement for quick and easy manual control of the radial positioning, relative to a pipe to be cut, of the one or more cutting tools, independent of the presence or absence of the pipe itself.

Turning to Figure 5, this shows by way of example one manner in which each of the cutting tools may be arranged on the frame so as to be radially moveable in the various ways required of it. (In the case illustrated here it happens to be the (right-hand) cutting- off tool 100b, but the other cutting tool 100a can be expected to be mounted and arranged likewise by means of its own arrangement of corresponding components.) The cutting tool 100b is mounted on a mounting plate 240 which is itself mounted onto the forward section 30a of the tool carrier ring of the frame (see further below). The tool 100b is attached to the mounting plate 240 via a parallel linkage 160, comprising a pair of rigid (e.g. metal) pivot arms 160 pivotally anchored at each end by pivot pins or bolts 180. (Any other suitable form of linkage, even a single-point linkage, may be possible, although that may be expected to be not as stable and thus possibly less preferred.) The upper end of the tool 102b is connected to the respective secondary piston rod of the associated secondary hydraulic cylinder 102b, which is itself anchored to an opposite section 30a of the tool carrier ring of the frame by inter-engaging dovetail formations at an upper dovetail fixing position 220a. Optionally the secondary hydraulic cylinder 102b may be fixed in place in its upper dovetail fixing position 220a by means of a locking screw or bolt 202. Thus, as the secondary hydraulic cylinder device is actuated (as described above) in a "push" or "pull" manner (as described above), the tool 100b moves with a traversing motion in a generally either downward or upward (as shown in Figure 5) direction, i.e. towards or away from a pipe located within the frame.

Although the parallel linkage 160 may, by its inherent nature, result in a small variation in the angle of incidence of the tool blade against the pipe, in practice this can be expected to be acceptable or its practical effect even negligible. This is not only because the maximum cut depth (i.e. maximum distance of radial travel) of the tool will in many cases be small and thus any such variation likewise relatively very small also, but more importantly any such variation will in any event be in the circumferential direction of the cut in the pipe wall, so can be expected not to be noticed or have any significant practical negative effect anyway.

The cutting tool 100b, carried on its mounting plate 240, is mounted on the forward section 30a of the tool carrier ring of the frame via a first species of blanking plate 260, as shown in Figure 5. This blanking plate 260 has a unique arrangement of inter- engageable dovetail formations on its opposite faces, by which not only the mounting plate 240 can be attached to the blanking plate 260, but also the blanking plate 260 itself can be attached to the frame section 30a, as shown. If desired or appropriate the respective mounting 240 and blanking 260 plates may optionally be fixed in place by means of respective locking screws or bolts 242, 262.

As shown in Figure 5, this first species of blanking plate 260 anchors the mounting plate - and thus the cutting tool 100b - in a first relative radial position (with respect to the pipe), in conjunction with the anchoring of the secondary hydraulic cylinder 102b in its upper dovetail fixing position 220a, as above. When it is desired to change the set-up of the apparatus so that the tool 100b is located in a different relative radial position (i.e. with a different range of radial distance of travel) - such as may well be the case with a pipe of a significantly different diameter - it is a relatively straightforward matter to replace the first blanking plate 260 with a different one, namely a second species of blanking plate 270, as shown in Figure 6. This second form of blanking plate 270 has its own, different, construction and configuration, including a different arrangement of dovetail formations, which enable it to be anchored to the frame section 30a in a different radial location, as shown by way of example in Figure 6. Starting from Figure 5 therefore, having first disengaged the secondary hydraulic cylinder 102b from its upper dovetail fixing position 220a, the first blanking plate 260 can simply be removed by first removing the tool's mounting plate 240 and then the first blanking plate 260 itself by unscrewing the relevant anchoring screws or bolts 242, 262, and then the new second blanking plate 270 can be installed in place of the first one 260 by simply re-assembling the combined assembly, including finally re-attaching the secondary hydraulic cylinder 102b in a middle 220b dovetail fixing position, as shown in Figure 6. Thus, by virtue of the different dovetail formation arrangement of the second blanking plate 270 and the variable dovetail fixing position of the secondary hydraulic cylinder 102b, the resulting mounting location of the tool 100b carried on its mounting plate 240 is moved to a new radial location.

Going slightly further, if for example it is desired to move the tool 100b carried on its mounting plate 240 to a third, even lower, radial position/location, as defined by the secondary hydraulic cylinder 102b being anchored in a lower dovetail fixing position 220c, then this may be accomplished by use of a third species of blanking plate (not shown), with yet another different arrangement of dovetail formations to allow it to be attached to the frame section 30a in yet another, even lower, unique radial position/location, in a corresponding manner as described above.

It will be readily appreciated that any number of different radial mounting positions/locations of the tool's mounting plate 240 is possible, by appropriate selection of the right form and configuration of blanking plate. Thus, in order to be prepared for being able to accommodate a large variety of different pipe diameters, it may be expected that a complete kit of components provided for day-to-day use of the apparatus may include a plurality of (e.g. 2, 3, 4, or even more) different such blanking plates 260, 270, etc, each providing for a unique radial mounting location/position of the tool's mounting plate 240 when installed in the apparatus in the manner shown and described with reference to Figures 5 and 6.

It is of course possible that any given single species of blanking plate may itself, by virtue of its particular arrangement of dovetail formations, be able to inherently provide more than one unique radial mounting position for the tool's mounting plate 240, provided the latter's complementary dovetail formations are arranged appropriately, without the need to resort necessarily to a completely different blanking plate, as will be appreciated by the person skilled in the art.

Turning to Figures 7(a) and 7(b), these figures show schematically by way of example one manner in which the overall tool positioning mechanism of Figure 5 (or Figure 6) is moveable in an axial, i.e. longitudinal (relative to the pipe), direction. This form of adjustment is similar to the manner of positioning of a tool of a conventional lathe. In the case of preferred embodiments of this invention however, this form of adjustment may be useful and/or important in cases where two or more cutting tools are provided, and it may often be desired to alter or adjust the axial spacing between such tools. This may be particularly useful for example in the case of the above-described tools 100a and 100b, where the preferred tool 100a for performing a grooving operation in the outer wall of a pipe to be cut-off by tool 100b may need to be selected to be a particular distance from the pipe's open cut end.

As shown in Figures 7(a) and 7(b), the opposite frame sections 30a on which the components of the tool positioning mechanism are mounted terminate in terminal frame parts 310, 312, each of which is mounted on a pair of longitudinally extending upper and lower mounting rods 320a; 320b along which the respective frame parts 310, 312 are readily slidable (e.g. by manual manipulation). Each frame part 310, 312 is further mounted on a central locking rod 330a; 330b, which is for example screw-threaded and lockable by virtue of a separate locking nut (e.g. 340) located within the relevant frame part (e.g. 310). Thus, by conventional unscrewing or loosening of the screw-threaded locking rod 330a and/or locking nut 340, then manually moving or adjusting the relevant axial /longitudinal position of the overall tool positioning assembly to the desired new axial/longitudinal location, and finally re-locking the rod/nut combination, any particular desired axial/longitudinal positioning of the assembly can be achieved.

It is to be understood that the above description of one or more preferred embodiments of the invention in terms of its various features and aspects has been by way of non- limiting example(s) only, and various modifications may be made from that which has been specifically described and illustrated whilst remaining within the scope of the invention as claimed.

Claims

1. A pipe cutting apparatus comprising a frame for receiving a pipe to be cut, and cutting means carried by the frame, the cutting means and the pipe being relatively rotatable with respect to each other to perform a cut, wherein the cutting means comprises at least one cutting tool and a positioning mechanism for controlling the relative position of the cutting tool with respect to the pipe,

wherein the positioning mechanism comprises:

(i) secondary biasing means attached to the cutting tool;

(ii) force transmission means connected to the secondary biasing means; and

wherein the actuation means is selectively actuatable either to cause the primary biasing means to apply biasing force, via the force transmission means, to the secondary biasing means so as to advance the cutting tool into cutting relationship with the pipe, or to enable the primary biasing means to receive biasing force, via the force transmission means, from the secondary biasing means so as to retract the cutting tool out of cutting relationship with the pipe.

2. A pipe cutting apparatus according to claim 1 , wherein the primary biasing means comprises at least one compression spring.

3. A pipe cutting apparatus according to claim 1 or claim 2, wherein the or each secondary biasing means comprises at least one compression spring.

4. A pipe cutting apparatus according to any one of claims 1 to 3, wherein the force transmission means comprises a hydraulic device.

5. A pipe cutting apparatus according to claim 4, wherein the hydraulic device comprises a primary hydraulic cylinder associated with the primary biasing means and a or a respective secondary hydraulic cylinder associated with the or each secondary biasing means and in fluid communication with the primary hydraulic cylinder.

6. A pipe cutting apparatus according to claim 5, wherein the primary biasing means is mounted within the primary hydraulic cylinder, and the or each secondary biasing means is mounted within the or a respective secondary hydraulic cylinder.

7. A pipe cutting apparatus according to any one of the preceding claims, wherein the actuation means of the positioning mechanism comprises a manually operable pivotable lever, which is selectively configurable into either an advanced position, in which the primary biasing means imparts biasing force in a forward direction, via the force transmission means, to the or each secondary biasing means and thus to the cutting tool(s) to move it/them into its/their cutting relationship with respect to a pipe mounted in the frame, or alternatively a withdrawn position, in which the or each secondary biasing means is permitted to impart biasing force in a reverse direction, via the force transmission means, to the primary biasing means and thus to retract the or each cutting tool from its cutting relationship with respect to the pipe.

8. A pipe cutting apparatus according to any one of the preceding claims, wherein the cutting means comprises a plurality of cutting tools, each cutting tool having a different construction or configuration from the other(s), such that each cutting tool is designed to perform a specific cutting or machining operation different from the other(s).

9. A pipe cutting apparatus according to claim 8, wherein the positioning mechanism comprises:

10. A pipe cutting apparatus according to claim 9, wherein the frame comprises radially adjustable gripping means for altering the effective internal diameter of the space inside the frame, in order that the frame can accommodate and securely clamp pipes of different diameters.

11. A pipe cutting apparatus according to any one of the preceding claims, further including at least one counter-support device mounted substantially diametrically opposite the or each cutting tool.

12. A pipe cutting apparatus according to any one of the preceding claims, wherein the frame comprises a plurality of mounting means, each at a different radial pitch, onto (or into engagement with) any one of which the cutting means are mountable to provide for a predefined maximum and minimum radial position of the cutting tool(s), and thus distance of radial travel thereof, with respect to the pipe to be mounted within the frame.

13. A pipe cutting apparatus according to claim 12, wherein the cutting means are carried on a mounting plate and the mounting plate is attached to the frame via a moveable or interchangeable blanking plate.

14. A pipe cutting apparatus according to claim 13, wherein the blanking plate is a blanking plate selected from a plurality of differently constructed and/or configured blanking plates that each define, by virtue of its own unique arrangement of plural mounting formations, a unique radial position/location with respect to the frame.

15. A pipe cutting apparatus according to any one of the preceding claims, wherein the cutting means are mounted with respect to the frame in an axially (i.e. longitudinally) variable and/or adjustable position.

16. In combination, a pipe cutting apparatus according to any one of claims 1 to 15 together with a pipe to be cut or machined, the pipe being mounted within the frame of the apparatus.

17. A method of cutting or machining a pipe, comprising:

(i) placing the pipe to be cut within the frame of an apparatus according to any one of claims 1 to 15;

(ii) actuating the actuation means of the positioning mechanism to cause the primary biasing means to apply biasing force, via the force transmission means, to the secondary biasing means attached to the cutting tool, whereby the cutting tool is advanced into cutting relationship with the pipe; and

(iii) rotating the cutting means with respect to the pipe while the cutting means is biased into its cutting relationship with the pipe under the combined biasing forces of the primary and secondary biasing means.

18. A method according to claim 17, further including the step of:

(iv) de-actuating the actuation means to cause the primary biasing means to receive biasing force in a reverse direction, via the force transmission means, from the secondary biasing means attached to the cutting tool, whereby the cutting tool is retracted from its cutting relationship with the pipe.

19. A method according to claim 17 or claim 18, which is a method of performing any one or any combination of the following cutting or machining operations:

- complete cutting-through of the pipe wall;

- partial cutting-through of an outer surface or wall of the pipe;

- stripping of one or more outer layers from the outer surface of the pipe, to allow the pipe to be joined to another by butt-fusion;

- removal of irregularities from the outer surface of the pipe, for providing a cut end of the pipe with a clean, smooth outer surface of substantially uniform diameter to allow the pipe to be joined to another by electro-fusion;

- bevelling, chamfering or other shaping of the edge(s) of a cut pipe end, mouth or lip.

20. A pipe cutting apparatus, or the combination of a pipe cutting apparatus together with a pipe to be cut or machined, or a method of cutting or machining a pipe, substantially as described herein with reference to the accompanying drawings.