AU646138B2 - Method and apparatus for producing bores - Google Patents

Description

AUSTRALIA

Patents Act 1990q COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant: Actual Inventor(s): Address for Service: JESTALAN PTY LTD RSSFOR SERVICE ALTE RED William Wray Halliday,Ao

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Ian Wesley Armstrong, ry Louis i- A9xne adneg Grant Alexander Friend, CULLEN CO. Ra.n Trado6 Ma- At-toarne-ys, 234 Quen -S-t-et, 7- 1e% Austral~~'.3LI1\ Cor&,,Ao~ *brN,e METHOD AND APPARATUS FOR PRODUCING

BORES

tG Invention Title:

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Details of Associated Provisional Applications: No. PK4355 The following statemen is a full description of this invention, including the best method of performing it known to us.

2 THIS INVENTION is concerned with a method and apparatus for enlarging bores in metallic objects.

The invention is particularly, although not exclusively, suitable for the formation of bores in objects prior to a reaming or sleeving operation.

For the sake of simplicity the following description of' both the invention and prior art bore formation is illustrated by reference to the sleeving of hydraulic cylinders however it should be understood that the nvention is applicable to other applications.

In the refurbishment of hydraulic cylinders such as automotive clutch and brake master, wheel and slave cylinders, it is customary to bore out the cylinder body and insert therein brass or stainless steel sleeve of the required internal diameter. Such cylinders comprise a wide variety of irregular external shapes and dimensions and may comprise blind or open ended bores.

Hitherto, the main techniques employed in enlarging cylinder bores prior to resleeving comprised: machining with a single point cutting tool in an adjustable boring head, or, core drilling with a fluted drill bit followed by reaming. In both cases, these techniques are usually carried out in a lathe or boring machine and both techniques possess substantial disadvantages in terms of high labour content and inherent inaccuracies.

Machining with a cutting tool is generally limited to relatively short cylinders with a relatively large internal diameter. ,jn long cylinders with a narrow bore the cutting tool support shaft is prone to "chatter" due to flexure in the cutting tool support shaft and this leads to difficulty in controlling bore finish quality and size. Further, as the cylinders possess one or more radial fluid ports in the body in communication with the bore, chipping of the cutting tool point is quite common as it traverses.-the fluid port aperture and comes into contact with the trailing edge of the aperture.

Chipping of the tool point in turn gives rise to changes in the bore diameter and a poor surface finish.

New Zealand Patent No. 216343 describes alternative machining methods for cylinder sleeving techniques. In one method, the bore of the cast iron or aluminium alloy cylinder body is machined as described above to produce an enlarged bore. A stainless steel sleeve is then pressed into the bore, the sleeve is then "bored out" (presumably with a core drill), S' the radial fluid ports are drilled and then the sleeve is machined out to the required diameter. This method clearly possesses all of the prior art problems addressed above.

A second method described in New Zealand Patent No.

216343 comprises preforming the sleeve by first machining the external diameter and then machining the internal surface of the sleeve to the required final diameter. Given that the wall thickness of the finished sleeve is typically of the order of 1-1.25mm it is considered that in the absence of a complex and time consuming method of supporting the thin walled sleeve, the combined effects of flexure of the tool bar and the tubular sleeve would give rise to considerable 4 inaccuracies in both dimensions and "roundness" of the inner bore of the sleeve. The sleeve is then press fitted int a previously machined cylinder body and then the radial fluid ports are drilled through the sleeve wall. As the drilling of the sleeve wall gives rise to inwardly directed burrs, these must be removed by yet a further operation such as honing or the like to avoid subsequent damage to a piston slidable in the cylinder.

Core drilling followed by reaming is an alternative process for boring cylinders but again suffers from a number of serious disadvantages.

With this technique, the cylinder bore is first '11. enlarged by a three or four flute core drill. The drill bit is then removed from the lathe chuck (or the tool post on the sliding carriage) and an adjustable floating blade reamer or adjustable "Coventry" reamer inserted in its place prior to reaming the cylinder bore. A difficulty associated with floating blade reamers how-ver is that they tend to produce a ridge on the bore surface in a position opposite any radial fluid ports traversed by the reamer blades due to a self compensating effect.

Apart from the high labour content associated with tool changes the main disadvantage of core drilling and reaming is the high capital cost in obtaining a wide range of core drills of non standard length and diameter as well as a wide range of expensive adjustable reamers which require grinding from a limited range of standard sizes to suit the reaming task required. In addition these adjustable reamers usually require ground down morse taper extension sleeves to suit longer cylinders.

Although it has been proposed to manufacture specially designed multi-bladed tungsten tipped reamers to overcome the problems outlined above, these special reamers while less expensive, were nonadjustable and therefore a large number of reamers were required to suit the plethora of cylinder sizes.

In addition, as the cutting edge of the blades of these special reamers were parallel to the longitudinal axis, they were suitable only for cast iron cylinders and in any event the reaming times were unreasonably elongated due to the necessity for low revolution rate and low feed rates. A further problem 15 associated with fixed blade reamers is that after e *V sharpening they no longer retained their original •eg diameter and thus this necessitated replacement of a reamer unless a larger diameter reamer could be 2 sharpened to the required diameter.

20 All of the prior art cylinder boring techniques are considered to be deficient in terms of requiring S• one or more tool changes and relatively low machine and feed rates giving rise to a highly labour intensive operation. Further, as the external shapes of various automotive master, wheel and slave cylinders varies so greatly, considerable amounts of time are required to set up the cylinders in the lathe

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4 prior to machining, core drilling reaming anrd honing operations.

It is an aim of the present invention to overcome or ameliorate at least some of the problems and disadvantages associated with the enlargement of bores in metallic objects and to provide apparatus therefor.

It is a further aim of the invention to provide a method and apparatus for sleeving of cylinder bores.

According to one aspect of the invention there is provided an adjustable bore enlarging tool comprising:an elongate body portion; a cutting head portion, said cutting head portion comprising a plurality of support fingers extending in a direction parallel to a longitudinal rotational axis 15 of said tool, each said support finger including, on a *0 radially peripheral surface thereof, a cutting edge adjacent a free end of said support finger; and, expansion means to move said plurality of support fingers in a radially outward direction to selectively 20 vary the effective cutting diameter of said bore enlarging tool, said apparatus characterised in that .*So said plurality of supporting fingers are formed by o radial slots extending between the outer surface of said cutting head and a hollow aperture extending from a free end of said cutting head axially within said cutting head portion.

Suitably, the body portion comprises a ZFV Ivk\ cylindrical shape.

7 If required, the body portion may include a mounting shank at a free end opposite said cutting head.

Suitably, the cutting head portion is formed integrally with said body portion.

Suitably each said cutting face is rearwardly inclined at an angle of from 10 to 150 relative to a longitudinal axis of said body portion.

Preferably said cutting face is rearwardly inclined at an angle of 50 to 80 relative to a longitudinal axis of said body portion.

The expansion means suitably comprises a screw threaded member threadably engaged in hollow aperture within said cutting head portion.

15 Preferably said expansion means comprises a frusto-conical portion which engages an inner surface of said fingers, said frusto conical portion in use being adapted to selectively increase or decrease a cutting diameter of said bore enlarging tool.

20 According to yet a further aspect of the invention there is provided a mounting jig for enlarging a bore in an object, said apparatus

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comprising:a bore enlarging tool according to a first aspect of the invention; a base member adapted for mounting in association with a rotary machining device; r>Te a fixed mounting member and a movable mounting 8 member associated with said base member and adapted to engage an object therebetween in a predetermined juxtaposition relative to a rotational axis of said bore enlarging tool when mounted in said rotary machining device; and, alignment means to align a central axis of a bore in said object with said rotational axis of said bore enlarging tool.

Suitably said jig includes clamp means associated with said movable mounting 'member to selectively move said movable mounting member towards or away from said fixed mounting member to engage or disengage said object.

Said clamp means may comprise any suitable means 15 associated with said base member to move said movable member into engagement with an object located between said fixed and movable members.

The clamp means may comprise a screw threaded o shaft, a rotatable cam, a fluid powered ram, an adjustable toggle linkage or the like.

Preferably, said jig includes mounting adaptors •for association with either or both of said fixed and 9 movable mounting members.

*o The alignment mear.. may comprise a retractable mandrel mounted on a swingable arm associated with said base member.

Suitably means may be provided to introduce cutting fluid and/or compressed air into the bore of 9 the object during a bore enlarging procass.

According to another aspect of the invention there is provided a method of enlarging a bore in an object, said method comprising the steps of:mounting said object in a mounting jig according to one aspect of the invention sajd mounting jig being associated with a rotary machining apparatus; aligning a longitudinal axis of said bore of said object with a rotational axis of a bore enlarging tool according to a further aspect of the invention, said bore enlarging tool being mounted in a tool holder of said apparatus; and machining an enlarged bore in said object with said bore enlarging tool, said method characterised in that said bore enlarging tool is adapted to carry out simultaneously the functions of a core drill and a bore reamer.

S" Alignment of the axis of said bore is preferably effected by means of an alignment mandrel.

20 The alignment mandrel may be associated with the chuck of said apparatus or alternatively with said mounting jig.

Suitably, enlargement of the bore of said object is achieved by a single machining pass of said bore enlarging tool.

As used herein, the expression "rotary machining apparatus" means any apparatus in which relative rotational movement may be effected between a bore "V

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'N j 9a enlarging tool and an object having a bore to be enlarged, the apparatus also including means to selectively permit the bore enlarging tool to extend into or retract from the bore of the object. Such apparatus is well known in the art and may comprise a metal working lathe, a rotary boring machine, a radial drill press or the like.

In order that the various aspects of the invention may be more fully understood, reference will now be made to preferred embodiments illustrated in the accompanying drawings in which: FIG 1 is a side elevation of a mounting jig mounted in a lathe; FIG 2 is an enlarged cross sectional view showing 15 an irregularly shaped object mounted between the fixed and movable members of the jig; FIG 3 shows a part sectional side elevation of a boring tool; and FIG. 4 shows an end elevation of the boring tool illustrated in FIG. 3.

FIG. 5 illustrates an alternative embodiment of the invention.

In FIG. 1 the jig 1 comprises a base 2 mountable on a carriage 3, the carriage 3 in turn being slidable on a bed 4 of a metal turning lathe (not shown).

The jig 1 includes a fixed mounting member 5 and a movable mounting member 6 slidable on parallel bars 7 secured between fixed mounting member 5 and a support member 8 at the rear end of the jig. Movable mounting member 6 is selectively slidable along bars 7 by means of a screw threaded shaft 9 mounted at one end in a bearing block 10 attached to movable member 6.

A rotatable nut 11 journalled in a bearing housing 12 co-operates with thre-.led shaft 9 to selectively move movable member 6 towards or away from fixed mounting member An automotive brake master cylinder 13 is shown e* clamped between fixed and movable mounting members 5 and 6 20 respectively. A small pneumatic ram 14 having a retractable 0 S locking pin 15 is employed to lock nut 11 after the cylinder 13 or a like object to be bored is clamped between the mounting members 5 and 6. A switch 16 connected to a solenoid valve (not shown) is provided for rapid actuation of ram 14.

Bearing block 10 supports a fluid conduit 17 attached to which is a two way valve 18 in turn having inlets 19, 20 for respective connection to conduits connected to a source of cutting fluid and a source of compressed air.

At the front end 1A of jig 1 is positioned a rotary boring tool 21 mounted in the chuck 22 of a lathe (not shown).

In the process of enlarging a bore in an object, as exemplified in the present case by a method of sleeving an automotive brake cylinder, it is essential that the cylinder 13 is accurately aligned in the jig 1 before boring is commenced. For relatively long cylinders as shown, alignment is achieved by first mounting a mandrel (not shown) in the lathe chuck 22 and with the cylinder 13 held loosely between the opposed faces 5a, 6a of mounting members 5 and 6 the lathe carriage 3 is advanced towards the chuck 22 until the mandrel locates within the bore of cylinder 13 thus aligning the S• respective central axes of the mandrel and the cylinder bore.

With the cylinder body so aligned, nut 11 is rotated to advance movable mounting member 6 towards fixed member 5 to clamp cylinder 13 firmly between faces 5a and 6a. Switch 16 is then thrown to actuate ram 14 to lock nut 11 against rotation.

Carriage 3 is then moved rearwardly to retract the 2.0 mandrel from the bore of cylinder 13, The mandrel is then replaced in the lathe chuck 22 with a special boring tool 21 according to another aspect of the present invention and later described in detail. Boring tool 21, having an adjustable boring diameter is preferably pre-set to a required diameter however it could be adjusted after positioning in the lathe chuck.

With the boring tool 21 operating at an appropriate speed, carriage 3 is advanced towards the lathe chuck 22 until 12 it engages an adjustable stop 23 attached to the headstock or bed of the lathe. The position of the stop 23 is pre-set to control the boring depth of tool 21.

Carriage 3 is then retracted and it can be seen that the boring operation to produce an accurately dimensioned enlarged bore in cylinder 13 is effectively a one step operation compared with at least two steps in prior art boring and reaming processes.

Depending on the nature of the material of the brake cylinder 13, e.g. cast iron or aluminium alloy, valve 18 may be selectively actuated to introduce into the bore of the cylinder 13 a cutting fluid to act as a coolant/lubricant or compressed air to flush metal particles out of the cylinder bore during the boring operation.

The cylinder 3 is then sleeved with a thin walled metal tube, preferably stainless steel, having predetermined inside and outside diameters. The sleeving operation is S.conducted in a conventional manner by mechanically pressing the sleeve into the bore with or without a sealant or merely inserting the sleeve in a manual push fit manner with an adhesive.

In or6'r to illustrate in more detail the adaptability of the jig 1 to a very wide variety of automotive hydraulic master, wheel and slave cylinders. FIG. 2 shows an enlarged cross-sectional view of the forward portion of jig 1.

Fixed and movable mounting members 5 and 6 respectively each have mounted therein hardened metal annual sockets 25 with circular recesses adapted to receive a variety 13 of mounting adaptors.

The front mounting adaptors 26 generally comprise annular members with a central hole slightly larger than the desired bore diameter of the cylinder 27 clamped thereagainst.

As an alternative to a chuck mounted alignment mandrel described with reference to FIG. 1, front mounting adaptors 26 can receive a mounting mandrel 26a to align the cylinder 27 during the clamping operation. To ensure accurate alignment of the longitudinal axis of the bore of cylinder 27 and the rotational axis of a chuck mounted boring tool, sockets 25 are accurately positioned within mounting members 5 and 6 and front and rear mounting adaptors 26, 28 respectively are also accurately machined.

For irregularly shaped cylinders such as that illustrated by cylinder 27, the rear mounting adaptors are fabricated to a variety of shapes to support the irregularly shaped rear faces of the cylinders. In the embodiment shown, adaptor 28 includes a tapered shaft 29 with a pointed end which penetrates the rear inclined face 30 or locates in a previously formed centring recess therein of cylinder 27 when clamping pressure is applied via rear mounting member 6. Rear adaptors 28 may included recessed depressions having shapes .i complementary to the rear portions of cylinders to be bored or they may include projections having complementary or otherwise appropriate support surfaces.

For "blind" bores of the type shown in cylinder 27, the use of cutting fluid and/or compressed air via conduit 17 is not possible and thus valve 18 is placed in a neutral or 14 inactive position. Cutting fluid or compressed air for flushing purposes may be periodically introduced through radial apertures in cylinder 27.

FIGS. 3 and 4 illustrate the boring tool 21 described with reference to FIGS. 1 and 2.

In FIG. 3 the boring tool comprises a head portion and a shank portion 31. Shank portion 31 typically comprises a solid steel rod of circular or polygonal shape in cross section. The mounting end of the shank 31 (not shown) may comprise any conventional configuration for mounting in a lathe chuck, such configurations including a morse taper, plain cylindrical or faceted (polygonal) cylindrical mounts S" etc.

Head portion 30 comprises a plurality of longitudinally extending rearwardly tapered ridges 32 protruding generally radially from the surface of shank portion 31. As shown in FIG. 4 radially disposed slots 33 extend rearwardly towards the rear end of ridges 32 to form "finger" like members 34 in conjunction with a generally 2.n cylindrical aperture 35 extending longitudinally into the body of the boring tool along a rotational axis shown as 36 in FIG.

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In the region of the end face 37 of head portion aperture 35 has an outwardly tapered region 38 while the portion 39 of aperture 35 extending rearwardly thereof is screw threaded to receive adjusting bolt 40 shown in FIG. 3A.

Adjusting bolt 40 comprises a screw threaded cylindrical portion 41 and a frusto-conical head 42 with a hexagonal recess therein (not shown) to receive an Allen key or '-he like. The frusto conical head 42 is tapered so as to be complementary to the tapered region 38 of aperture By advancing bolt 40 into aperture 35, the fingers 34A, 34B and 34C are biased outwardly in a radial direction while being supported against compressive forces in use by the tapered head 42. In this manner the boring tool 21 of FIGS.

1, 3 and 4 is adjustable with a great degree of accuracy with very fine tolerances to a desired boring diameter.

At the front end of head portion 30 which preferably is comprised of high speed steel, are raised projections 43 on ridges 32 which support hardened steel or alloy cutting teeth 44 secured in sockets 45 on the leading faces 46 of projections 43.

Table 1 which follows sets out effective and preferred angles and angle ranges for structural features of the boring tool according to the invention.

TABLE 1 Adjustable Boring Tool Detail .b Description Angle Preferred Angle Effective Angle Range Back Clearance Angle BC .025mm/25mm 0 to 0.38mm (.001/inch) (0 to 0.015"/inch) Front Clearance Angle FC 5° 20 to 100 Cutting Approach Angle AA 50 00 to 45 0 Radial Clearance Angle RC 00 for 0.1mm 00 for 0.1 to 1.Smm then 120 then 10° to Radial Rake Angle RR 0° -30 to Back Rake Angle BR 60 00 to Adjusting Screw Taperangle ST 300 20° to .4t4 4 S1

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5 4 In fabrication of the boring tool according to the invention it is preferred that the cutting teeth be spaced irregularly rather than regularly about the periphery of head portion 30 to avoid "chattering" of the boring tool when in use and the production of ridge-like projections opposite any apertures in the bore.

Table 2 hereunder represents typical values for the angular variation from even radial spacing of teeth in boring tools according to the invention.

TABLE 2 TEETH SPACING Number of Tooth Number Teeth on (Angular Variation Degrees) Tool 1 2 3 4 5 6 7 8 9 10 11 12 3 0 -0.7 +1.2 4 0 -1.8 +0.9 -1.4 0 -0.5 +0.7 -1.2 6 0 -0.9 +1.2 -1.6 +1.4 -1.2 7 0 -0.5 +0.4 -0.4 +0.7 -0.2 8 0 -0.7 +1.2 -0.5 +0.9 -1.4 +0.5 -0.7 9 0 -0.7 +1.2 -1.6 +1.4 -1.2 +0.5 -0.7 0 -0.5 +0.7 -1.2 +0.5 -0.5 +0.7 -0.5 +1.2 -0.2 11 0 -0.9 +0.9 -0.5 +0.5 -0.7 +0.7 -0.5 +0.7 -0.5 +0.7 12 0 -0.9 +0.9 -0.2 +0.7 -0.9 +0.9 -0.7 +0.5 -0.5 +0.7 -0.9 FIG 5. illustrates an alternative embodiment to the apparatus and method aspects of the invention.

For the sake of clarity, FIG 5 shows in phantom a schematic plan view of the jig 1 of FIG 1 to which an alternative bore alignment means is attached.

In FIG 5 a retractable mandrel support apparatus is attached to jig 51 by means of bolts or set screws 52 securing support brackets 53 to the base 54 of jig 51.

Brackets 53 secure a hardened and ground guide rod Slidably located in brackets 53 is a hardened and ground bar 56 located in sealed linear motion bearings 57 which, in turn, are located in Torrington races 58 in sealed housings mounted on brackets 53. Resilient buffers 59 are mounted on bar 56 to limit the slidable movement of bar 56 in «e bearings 57 and to cushion any impact with the bearing **ue* housings.

Mounted on the end of bar 56 is a mandrel support arm 60 having a telescopic arm 61 securable in arm 60 by means of clamp 62. A mandrel mounting head 63 locates a removable '"2O alignment mandrel 64 and a handle 65 is provided to operate

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the retractable mandrel support apparatus.

A cam adjustable roller 66 is provided at one end of mandrel support arm 60 and co-acts with the underside of guide rod 55 to slidably support mandrel support arm 60 whilst in the extended position shown. A resilient buffer 67 is provided to support mandrel support arm 60 on the upper side of guide rod 55 whilst in the retracted position.

The retractable mandrel support apparatus 50 is particularly suitable where a large number of bores of the same diameter are to be made in hydraulic cylinders or the like. In contrast to the previously described method which involved removal of the cutting tool from the lathe chuck, insertion of the mandrel and Plignment of the cylinder, then removal of the mandrel and reinsertion of the cutting tool, this apparatus permits the cutting too., to remain in the lathe chuck at all times.

After inserting in the lathe chuck (not shown) a boring tool 68 of the required diameter, mandrel support arm is swing into the extended position as shown by pivoting about the rotational axis of rod 56. Initially, the mandrel to mounting head is aligned with the rotational axis of tool 68 by means of clamp 62 and cam adjustable roller.

A mandrel 64 is then located in head 63 and by means of handle 65 the mandrel support arm is moved towards the jig 51 and through the apertured cylinder mounting adaptor (not shown) in the front fixed mounting member 69 until it engages in the bore of the cylinder to be bored. As described previously the movable mounting member 70 is advanced towards fixed mounting member 69 to clamp the cylinder (not shown).

After the cylinder is clamped the mandrel 64 is removed from the cylinder bore by sliding arm 60 and rod 56 towards the lathe headstock and when the mandrel 64 is clear of jig 51, arm 60 :etacted by rotating upwardly about the longitudinal axis of rod 56.

The cylinder boring process is then carried out as previously described with reference to FIGS 1 and 2.

19 It readily will be clear to a skilled addressee that the various aspects of the invention in the method of enlarging bores in objects, the supporting jig for such objects and the boring tool all contribute to improvements in their respective prior art counterparts to overcome or at least ameliorate the known prior art disadvantages.

The invention, in its various aspects provides a method and apparatus which give rise to reduced labour costs and lower capital costs associated with bore enlargement procedures and apparatus while nevertheless maintaining the high degree of precision required in such procedures.

While the present invention has been exemplified by reference to bore enlargements of automotive hydraulic cylinders to facilitate sleeving of such cylinders, it should be understood that the invention is not so limited and is applicable to precision bore enlargement of articles on a "one-off" or repetitive basis e.g. precision bore formation in castings etc.

4 It will be readily apparent to a skilled addressee that many modifications and variations may be made to the various aspects of the invention without departing from spirit and scope thereof.

Claims (16)

1. An adjustable bore enlarging tool comprising:- an elongate body portion; a cutting head portion, said cutting head portion comprising a plurality of support fingers extending in a direction parallel to a longitudinal rotational axis of said tool, each said support finger including, on a radially peripheral surface thereof, a cutting edge adjacent a free end of said support finger; and, expansion means to move said plurality of support fingers in a radially outward direction to selectively vary the effective cutting diameter of said bore enlarging tool, said apparatus characterised in that o said plurality of supporting fingers are formed by radial slots extending between the outer surface of said cutting head and a hollow aperture extending from a free end of said cutting head axially within said cutting head portion.

2. A boring tool as claimed in claim 1 wherein each 20 said cutting edge has a ,cutting approach angle within the range of from 0° to

3. A boring tool as claimed in claim 2 wherein the cutting approach angle is within the range of from to

4. A boring tool as claimed in any preceding claim wherein a cutting face associated with each said cutting edge is rearwardly inclined at an angle of 1/<y from 50 to 80 relative to a longitudinal :-i3 of said body portion.

A boring tool as claimed in any preceding claim wherein said expansion means comprises a screw threaded member threadably engageable in a hollow aperture between said support fingers, said screw threaded member including a frusto-conical surface engageable with said support fingers to selectively increase or decrease the effective cutting diameter by radial expansion or contraction of said plurality of fingers. *i

6. A mounting jig for enlarging a bore in an object, said apparatus comprising:- a bore enlarging tool according to any one of claims 1 to a base member adapted for mounting in association S* with a rotary machining device; 0 a fixed mounting member and a movable mounting member associated with said base member and adapted to engage an object therebetween in a predetermined 20 juxtaposition relative to a rotational axis of said bore enlarging tool when mounted in said rotary machining device; and, alignment means to align a central axis of a bore in said object with said rotational axis of said bore enlarging tool.

7. A mounting jig as claimed in claim 6 wherein clamp means is associated with said movable mounting /y member to frictionally engage said object between said fixed and movable mounting members.

8. A mounting jig as claimed in claim 6 or claim 8 wherein said alignment means comprises a retractable mandrel mounted on a swingable arm associated wi th said base.

9. A method of enlarging a bore in an object, said method comprising the steps of:- mounting said object in a mounting jig according to any one of claims 6 to 8, said mounting jig being associated with a rotary machining apparatus; •0 aligning a longitudinal axis of said bore of said object with a rotational axis of a bore enlarging tool according to any one of claims 1 to 5, said bore enlarging tool being mounted in a tool holder of said apparatus; and machining .an enlarged bore in said object with said bore enlarging tool, said method characterised in that said bore enlarging tool is adapted to carry out simultaneously the functions of a core drill and a bore reamer.

A method as claimed in claim 9 wherein enlargement of the bore in said object is achieved b. a single pass of said bore enlarging tool.

11. A method as claimed in claim 9 or claim wherein said object comprises an automotive hydraulic brake or clutch cylinder.

12. A method of re-sleeving an automotive hydraulic brake or clutch cylinder comprising the steps of: 23 enlarging a bore of said brake or clutch cylinder according to the method of claim 9; and, locating within an enlarged bore of said brake or clutch cylinder a tubular sleeve of predetermined longitudinal and diametrical dimensions.

13. A bore enlarging tool substantially as hereinbefore described with reference to any one of FIGS 3, 3a or 4 of the accompanying drawings.

14. An apparatus for enlarging a bore in an object substantially as hereinbefore described with reference to any one of FIGS 1, 2 or 5 of the accompanying drawings.

15. A method of enlarging a bore in an object substantially as hereinbefore described with reference to any one of FIGS 1 to 5 of the accompanying drawings.

16. A method of re-oleeving an automotive hydraulic clutch or brake cylinder substantially as hereinbefore described with reference to the description of the 20 preferred embodiments of .the invention. DATED this Ninth -ay of November 1993 JESTALAN PTY LTD By their Patent Attorneys FISHER KELLY ABSTRACT A rotary tool (30) for enlargement of bores in object such as automotive brake and clutch cylinders (13) prior to re- sleeving permits precision bore enlargement in a single pass by combining the advantages of a core drill and a bore reamer. The bore enlargement tool (30) comprises a cutting head portion (32) with a plurality of radially expandable fingers (34) each supporting a cutting face (44) adjacent a free end thereof. The bore enlargement tool (30) is used in S combination with a jig to support braker and clutch cylinders (13) of varying configurations as an initial step in Soe a re-sleeving method. 0* 0 0 0 0