GB1583860A

GB1583860A - Core drills

Info

Publication number: GB1583860A
Application number: GB3483976A
Authority: GB
Original assignee: Moppes & Sons Ltd L Van
Current assignee: Moppes & Sons Ltd L Van
Priority date: 1976-08-20
Filing date: 1976-08-20
Publication date: 1981-02-04

Description

(54) IMPROVEMENTS IN AND RELATING TO CORE DRILLS (71) We L. M. VAN MOPPES & SONS LIMITED, a British Company, of Lister Road, Basingstoke, Hampshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to core drills of the type comprising a cutting head mounted on a tubular metal support.

Such drills are required in a variety of sizes from say 6 mm to 1 metre or even 1 l metres or more, and are largely used in the construction industry for example for drilling holes through reinforced concrete to take service conduits. Another use is where it is desired to cut a hole such as a doorway into a wall. In such a case, a series of holes say 10 cm in diameter can be drilled around the outline of the opening to be formed, and the panel blocking the opening can then be removed easily with the minimum of shock disturbance to the remainder of the wall.

Hitherto such drills have been made using drawn tube. The use of drawn tube involves certain disadvantages. Firstly, because of the very wide variety of drill sizes which may be required, it is necessary for the drill manufacturer to carry large stocks of tubes of different sizes some of which may be required only very rarely. This is wasteful of capital. Secondly, in order to reduce the amount of material which is cut away during the actual drilling operation, and thus the time and power consumed by the operation, it is desirable that the tubes should have walls which are as thin as possible, consistent with the strength required to support the cutting head. Thin walled drawn tube of the required quality is commercially available in diameters up to say 10 cm, but above this diameter, the wall thickness of commercially available drawn tube is too great for optimum performance.

Of course tubes of the required diameter and wall thickness could be specially ordered, but the tube manufacturer could only supply these at high unit cost or in large quantities, and this would again involve heavy expenditure on the part of the drill manufacturer.

Accordingly, drills of at least the larger sizes have hitherto been made by machining standard commercially available tubes to the required wall thickness. Machining a large diameter thin-welled tube is a highly skilled and time consuming process, and distortion of the tube during machining is an ever present peril. For example, if a customer requires a 35 cm diameter coredrill, it may take say half an hour to draw tube of the required size from stock and cut it to length, but the process of machining the inside and outside diameters to size may well take fourteen hours.

It is an object of the present invention to provide a core-drill of a novel construction which allows such drills conveniently to be made to a wide variety of sizes without the necessity of storing large stocks of tubing.

According to the present invention, there is provided a core drill comprising a cutting head formed by at least one cutting element mounted on a tubular metal support, which support comprises at least one tube formed of at least one rolled metal sheet and has a construction in which the tube wall is formed of at least one rolled metal sheet and has a construction in which the tube wall is formed by at least two sheet-thicknesses and in which each end of said at least one sheet is secured lap-wise to another metal sheet portion of the rolled tube to leave substantially cylindrical inner and outer faces.

Thus it will be seen that by making a core drill in accordance with the present invention, there is no need to carry large stocks of tubing of different sizes.

Though it is not envisaged that core drills of less than say 2.5 cm diameter would normally be made in this way, drills of any size can be made using the same stock sheet material.

In some preferred embodiments of the invention, the or at least one said tube is formed by a single spirally rolled sheet of metal. It is not necessary that such sheet should be formed with tapered or chamfered ends in order to present substantially cylindrical inner and outer faces of the tube thus formed, indeed it is preferred that there should be a joggle in the medial portion of the sheet at the or each place where it passes over that end of the sheet which is on the inside of the tube and into which the other end of the sheet nests on the outside of the tube. Each of these features reduces the time necessary for forming the tube.

In some embodiments of the invention, said support comprises a single said tube.

In the case of a drill whose support is a single spirally rolled tube, it is preferred to to locate the cutting head at a particular end so that when the drill is rotated clockwise in use the outer sheet end of the drill will trail.

In other preferred embodiments, a said tube is formed from at least two cylindrically rolled sheets which nest one inside the other. In such embodiments it is preferred that the two ends of the outer sheet should abut. Preferably also the two ends of the inner sheet should about. Advantageously the meeting ends of the separate rolled sheets are equilly spaced about the periphery of the tube.

The free ends of the sheet metal from which a said tube is rolled may be secured in any convenient manner, for example by gluing, but it is preferred that they should be secured by spot-welding.

The total wall thickness of the drill tube may be as desired. For some purposes, comparatively thick-walled tubes are required, and the total wall thickness may be 1 cm or more, but the advantage afforded by constructing a core-drill in accordance with the invention are particularly manifest for drills whose tubes each have a total wall thickness of 3mm or less, though for the large diameter drills, say 60 cm to 150 cm, a total wall thickness of up to 5 mm may be desirable.

It is especially convenient to form a drill tube in accordance with the invention from sheet metal whose thickness is between 0.5 mm and 1.5mm.

The sheet metal used is preferably mild steel. It is preferred that mild steel should be treated, e.g. galvanised, to inhibit rust formation at least prior to use of the drill.

In order to prolong the life of the cutting head it is generally desirable to cool it and/ or lubricate it during the drilling operation, and this has hitherto been done by providing an adaptor for the core drill which has an axial passage through which fluid can be pumped to the cylindrical space enclosed by the drill.

While satisfactory for small diameter drills, this method becomes inefficient for larger diameter drills, and it is a further object of the present invention to provide, in certain preferred embodiments thereof, a core drill whose cutting head can be more efficiently cooled and/or lubricated.

Accordingly, the present invention further provides a core drill as above defined which is characterised in that said tubular support comprises inner and outer tubes (at least one of which is rolled tube as hereinbefore specified) held. concentrically spaced apart by intervening spacer members and said cutting head defines one or more openings through which fluid introduced into the inner tube space can escape for cooling and! our lubricating the cutting head while the drill is in use.

This provides more satisfactory cooling of the cutting head.

The advantage of this preferred feature of the present invention is particularly apparent when the diameter of the core drill is 10 cm or more.

In some preferred embodiments of the invention, said cutting head comprises a plurality of said cutting elements which are circumferentially spaced apart to provide said openings.

In other preferred embodiments of the invention there is a single cutting element defining said cutting head which is provided with openings for the flow or said fluid.

The or each said cutting element preferably consists of a sintered metal matrix holding an abrasive material. Advantage ously said abrasive material is selected from: diamond dust, cubic boron nitride, corundum, silicon carbide, metal carbides and/or individually set diamonds. Such a cutting element may be formed in situ on the end of the tubular support.

Advantageously the or each cutting element comprises one or more projections constituting a key engaging the support to prevent radial displacement.

Preferably said support has one or more projections at its end which provide(s) a key engaging the or each cutting element against circumferential displacement.

It will be appreciated that for some drill sizes it may be convenient to use an inner or an outer thin-walled drawn tube of standard size, but preferably each said tube is formed of at least one rolled metal sheet.

In the case of a drill having a spirally rolled outer tube, it is preferred to locate the cutting head at a particular end so that when the drill is rotated clockwise in use the outer sheet end of the outer drill tube will trail.

Conversely, in the case of a drill having a spirally rolled inner tube, it is preferred that in use, the inner sheet end of the inner drill tube should trail.

The space between the inner and outer tubes of a core drill in accordance with preferred embodiments of the present invention is preferably between 2 and 5 mm across, so as to provide sufficient space for fluid flow while at the same time keeping the total thickness of the drill wall as low as possible.

Hitherto it has been normal practice to provide the interior of a core drill tube with a screw thread for engagement with an adaptor which in turn may be connected to a driving motor. In the case of a drill having a rolled (inner) tube, it is considered impracticable to provide such a thread as the wall thickness is not sufficient. The present invention therefore also provides an adaptor used in conjunction with a core drill whose (inner) tube has a plain cylindrical interior.

Such an adaptor comprises a body portion adapted for connection to a drive motor and a flange portion with a rebate defining a seat for the end of the tubular support of the core drill, at least one conically surfaced clamping member carried by screw means projecting through the flange portion, and an expansible generally circular member seated on the or each conical member, the arrangement being such that when said screw means is tightened the or each such generally circular member rides up its associated conical surface and is forced to expand radially so that it will engage the interior of the tubular support of the core drill which is seated against said flange portion.

Preferably said adaptor comprises at least one fluid flow passage communicating with the space between the tubes of said drill.

Said generally circular member may be a coil spring.

Alternatively it may be a single-coil ring.

In the case where a single-coil ring is used, it is preferred to use an additional such ring spaced from the first by a spacer ring, which additional single coil ring rides on a second conical surface.

In some embodiments there is a single said conically surfaced clamping member carried by a plurality of bolts projecting through the flange portion. In sllch a case and where two spaced single coil rings are used, it is convenient to provide the second conical surface on said flange portion.

In other embodiments said screw means is constituted as a plurality of bolts projecting through said flange and each such bolt carries a said conical member as a nut.

Preferably each such bolt also carries a conical sleeve.

There may be from three to five said bolts, but in the case of larger diameter drills, it is preferred that the spacing be tween said bolts should not exceed 20 cm.

For example in an adaptor for a 60 cm drill there may be as many as eight bolts.

Various preferred embodiments of the present invention will now be described in greater detail with reference to the accompanying diagrammatic drawings in which: Figures 1 and 2 are respectively rear end and side elevations of a first embodiment of Figures 3 and 4 are respectively front end and side elevations of a second embodiment of core drill; Figure 5 is a sectional view in a direction along the axis of a first embodiment of double-walled core drill constructed in accordance with the invention; Figure 6 is a section along the line VI-VI of Figure 55; Figure 7 shows a core drill and a driving adaptor therefor; and Figure 8 is an end elevation showing one arrangement of cutting head for a core drill in accordance with the invention.

In Figures 1 and 2, a core drill is formed by spirally rolling a mild steel sheet 1. It will be noted from Figure 1 that at the point where the sheet 1 leads from the inner surface to the outer surface of the tube this formed, there is a joggle 2 in which nest the inner end 3 and the outer end 4 of the sheet so that the tube has substantially continuous inner and outer surfaces.

The ends 3 and 4 of the sheet are lap-wise secured to medial portions of the sheet 1 to either side of the joggle 2. This may be done by gluing, but it is found especially convenient to spot-weld the tube for example at the points marked X in Figure 2.

The metal sheet 1 can conveniently be rolled into the tube in a single step on a bending machine comprising a steel bending roll bearing against a roll which is covered with a resilient material such as urethane.

Such machines are well known and have the advantage of bending the sheet blank right up to its end so that there is no need to preform the sheet blank to eliminate flat areas at its leading and trailing ends as is common with most three-roll bending machines. As the rolling proceeds, the joggle 2 will be formed automatically.

After formation of the tube a cutting head 5 is applied to one end. Such head may for example consist of diamond dust or other hard material, for example cubic boron nitride, corundum, silicon carbide or metal carbides or individually set diamonds, in a sintered metal matrix formed in situ on the end of the tube. Such head may be provided with waterways (not shown) but be otherwise continuous.

The preferred direction of rotation is shown in Figure 1 by the arrow, and this is arranged so that the outer end 4 of the sheet 1 from which the tube is formed will trail during use. The cutting head 5 is accordingly applied to that end of the tube which will allow this condition to obtain during clockwise rotation.

The tube is shown rolled in such a way that its walls are formed from two thicknesses of sheet. It will be appreciated that additional sheet material can be rolled so that the walls have three or more thicknesses of sheet if this is desired.

Figures 3 and 4 show an alternative coredrill again having tube walls formed of two thicknesses of sheet material. It will again be appreciated that extra thickness may be provided.

In Figure 3, a drill tube 6 is formed by cylindrically rolling two metal sheets into inner and outer tube portions respectively 7 and 8. These tube portions are assembled together as shown, and sizing discs (not shown) are inserted. The tubes are then squeezed in a clamp to achieve the desired size. For the best results, it is important that the ends 9 of the outer tube portion 8 should abut when this size is reached. It is not so important that the ends 10 of the inner tube portion 7 should abut though this is of course desirable. The sizing discs are removed, and ends 9 of the outer tube portion 8 are secured lapwise to the inner tube portion 7, for example by spotwelds X (Figure 4), and the ends 10 of the inner tube portion are likewise secured to the outer tube portion.

The front or head end of the tube 6 is castellated, and abrasive blocks 11 are secured, for example by brazing, into the crenels 12 to form the abrasive head.

It will be appreciated that the drill tubes described above may be made to any desired length, and that by appropriate choice of size of a bending roll they may be made to any desired diameter from say 2.5 cm to a metre of more.

In Figures 5 and 6, a core drill 13 is constituted by inner and outer tubes 14, 15 which are held in concentric arrangement by spacers 16. At plurality of cutting elements 17 is provided. Each such element comprises abrasive particles e.g. diamonds, cubic boron nitride or corundum in a matrix e.g. of sintered metal. The cutting elements 17 are of U-cross-section and span the inner and outer tubes 14, 15 so as to provide a key against radial displacement.

Alternatively, they may be of E- or cross-section with a portion projecting down between the inner and outer tubes. In order to key the cutting elements against circumferential displacement, the ends of the tubes 14, 15 may be castellated, and the cutting elements may be located in the crenels thus formed. The tubes 14, 15 and spacers 16 are suitably made of steel and may be secured together by spot-welding.

In order to supply cooling fluid to the cutting head of the drill a plurality of passages 18 are provided tbrough the inner tube 14 of the drill. Fluid flowing through these passages 18 can pass up the space between the inner and outer tubes, and can flow out between the cutting elements 17.

The number, shaping and spacing of these passages 18 is of minor importance provided that the total area is sufficient to allow the desired rate of flow of coolant.

It will be noted from Figure 5 that the inner and outer tubes 14, 15 are each made by cylindrically rolling two metal sheets 19, 20, 21, 22. These inner and outer tubes can be made in exactly the same way as the tube of the drill described with reference to Figures 3 and 4.

It will further be noted that the abutment lines 23 of the ends of the various sheets 19, 20, 21, 22 are equally spaced around the drill circumference and that they are each in register with a spacer 17 so that both ends of each sheet can be secured as by welding to a single spacer. It will also be appreciated that the ends of the outer sheet 22 of the outer tube 15 should abut for the best results, as should the ends of the inner sheet 19 of the inner tube 14.

Since the outer sheet 20 of the inner tube 14 and the inner sheet 21 of the outer tube 15 will not be in direct contact with the material being cut it is not so important that their ends should abut, though this is of course desirable.

In a variant of the embodiment illustrated in Figures 5 and 6, one of the inner and outer tubes 14, 15 is made from a drawn tube. This may be found more convenient when it is possible to use a drawn tube of a readily available size.

In a further variant of this embodiment, one or both of the inner and outer tubes 14, 15 is made from a spirally rolled sheet.

Such a tube may be made as described with reference to the drill illustrated in Figures 1 and 2.

When a tube such as that shown in Figures 1 and 2 is incorporated in such a core dril there is a preferred direction of rotation. If the tube is to form the outer tube 15 of core drill, it is preferred that it should be arranged to rotate in use in such manner that the end 4 (Figure 1) at its outer surface trails. Conversely, if such a tube is to form an inner tube, than it is preferred that the end 3 (Figure 1) at its inner surface should trail.

In view of the larger stresses which will have to be borne in use by a larger diameter drill, it is often desirable for larger drills to have greater tube wall thicknesses, and it will be appreciated that the tube forms shown may be made to have any desired number of thicknesses of sheet metal in order to take account of this, so that a drill of any desired diameter may be built up using sheet stock of only one thickness.

The interior of the inner tube of a core drill in accordance with the present invention may be threaded to receive an adaptor for driving, but in general, tubes made by rolling sheet material may be too thin to take such a thread, and accordingly, two alternative forms of adaptor which can be used in conjuction with a core drill having a plain cylindrical interior are shown in Figures 7a and 7b.

In each of these Figures, an adaptor 24 has a body portion 25 provided with an interior screw thread 26 and a flanged portion 27 having a peripheral rebate 28 defining a seat for the end of a double walled core drill 29. This flanged portion is provided with a series of holes, for example three to five holes, to receive bolts 30 by the tightening of which the drill can be anchored to the adaptor. For the sake of simplicity, each tube of the drill 29 is shown as being of single thickness. It will be appreciated that at least one such tube must be a rolled tube, for example a tube rolled as described with reference to the drill illusti-ated in Figures 1 and 2 or 3 and 4.

In Figure 7a these bolts 30 engage a clamping ring 31 having a conical outer surface 32. A short coil spring 33 of the largest diameter which will conveniently fit inside the core drill 29 is located between the clamping ring 31 and the flanged portion 27 of the adaptor so that when bolts such as 30 are tightened, the spring 33 will be forced to ride up the conical surface 32 of the clamping ring so that it is wedged fast against the drill 29 which is thereby anchored to the adaptor.

In Figure 7b there is no large single clamping ring which is engaged by all the bolts 30, rather each bolt is provided with its own individual clamping arrangement which includes a conical sleeve 34 and a conical nut 35.

A pair of single-coil rings 36 separated by a spacer tube 37 are provided one on each of the sleeve 34 and nut 35. As the nut is tightened, these rings ride up their associated core 34 or 35 until they are wedged fast against the drill 29.

It will be appreciated that each arrangement of single-coil rings and spacer in Figure 7b could be replaced by a coil spring, and that the coil spring 33 in Figure 7a could be replaced by a single-coil ring held spaced from the flanged portion of the adaptor.

In order to feed cooling or lubricating fluid to the drill while this is in use, such fluid is caused to pass into the central screw threaded portion of the adaptor 24 in known manner. The screw threaded hollow terminates in a blank wall, and a number of passages 38 lead out from the hollow and register with holes 39 formed in the inner tube 40 of the core drill 29. Fluid then passes along the drill between its inner and outer tubes and exits at the cutting end via holes 41 formed in an otherwise continuous cutting element 42 (see also Figure 8).

In order to facilitate registration of the holes 39 with the passages 38, such holes may be formed as slots.

Alternatively or in addition, a circumferential groove may be formed in the flanged portion 27 of the adaptor, the passages 38 all terminating in such groove.

In a variant, the inner tube 40 of the core drill 29 is made shorter than the outer tube and is arranged so that it terminates below the level of the ends of the passages 38 shown in Figures 7a and 7b.

The cutting element 42 may for example consist of diamond dust or other hard material, for example cubic boron nitride or metal carbides or individually set diamonds in a sintered metal matrix formed in situ on the end of the tube. The holes 41 may be circular as shown or slots, or any other convenient shape.

It will be appreciated that the adaptors described and illustrated in Figure 7a ond 7b may equally be used in conjunction with a drill formed in accordance with the description of any of Figures 1 to 6, and that any of the features of the drill described with reference to Figures 7a and 7b may be incorporated in the drill previously described with reference to Figures 5 and 6.

Thus, in a particular example, a drill is provided with a plurality of cutting elements such as the elements 17 (Figures 5 and 6), and each of these elements has a number of cutting face discharge openings such as the openings 41 shown in Figure 8.

In another modification, the spacers, e.g.

the spacers 16 of Figure 5, are wider in proportion to the intervals between them, and in yet a further modification in cases where a number of discrete cutting elements is used, jets are provided between the cutting elements for the discharge of coolant in a direction substantially parallel with the axis of the drill.

Finally, one or both tubes, preferably the inner tube alone, is slotted at the working end so that large particles of abraded material can be accumulated therein without damage to the drill. This feature is particularly advantageous for accommodating sections of steel rods cut away when drilling reinforced concrete, and it also provides reservoirs for coolant.

WHAT WE CLAIM IS: 1. A core drill comprising a cutting head formed by at least one cutting element mounted on a tubular metal support

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. order to take account of this, so that a drill of any desired diameter may be built up using sheet stock of only one thickness. The interior of the inner tube of a core drill in accordance with the present invention may be threaded to receive an adaptor for driving, but in general, tubes made by rolling sheet material may be too thin to take such a thread, and accordingly, two alternative forms of adaptor which can be used in conjuction with a core drill having a plain cylindrical interior are shown in Figures 7a and 7b. In each of these Figures, an adaptor 24 has a body portion 25 provided with an interior screw thread 26 and a flanged portion 27 having a peripheral rebate 28 defining a seat for the end of a double walled core drill 29. This flanged portion is provided with a series of holes, for example three to five holes, to receive bolts 30 by the tightening of which the drill can be anchored to the adaptor. For the sake of simplicity, each tube of the drill 29 is shown as being of single thickness. It will be appreciated that at least one such tube must be a rolled tube, for example a tube rolled as described with reference to the drill illusti-ated in Figures 1 and 2 or 3 and 4. In Figure 7a these bolts 30 engage a clamping ring 31 having a conical outer surface 32. A short coil spring 33 of the largest diameter which will conveniently fit inside the core drill 29 is located between the clamping ring 31 and the flanged portion 27 of the adaptor so that when bolts such as 30 are tightened, the spring 33 will be forced to ride up the conical surface 32 of the clamping ring so that it is wedged fast against the drill 29 which is thereby anchored to the adaptor. In Figure 7b there is no large single clamping ring which is engaged by all the bolts 30, rather each bolt is provided with its own individual clamping arrangement which includes a conical sleeve 34 and a conical nut 35. A pair of single-coil rings 36 separated by a spacer tube 37 are provided one on each of the sleeve 34 and nut 35. As the nut is tightened, these rings ride up their associated core 34 or 35 until they are wedged fast against the drill 29. It will be appreciated that each arrangement of single-coil rings and spacer in Figure 7b could be replaced by a coil spring, and that the coil spring 33 in Figure 7a could be replaced by a single-coil ring held spaced from the flanged portion of the adaptor. In order to feed cooling or lubricating fluid to the drill while this is in use, such fluid is caused to pass into the central screw threaded portion of the adaptor 24 in known manner. The screw threaded hollow terminates in a blank wall, and a number of passages 38 lead out from the hollow and register with holes 39 formed in the inner tube 40 of the core drill 29. Fluid then passes along the drill between its inner and outer tubes and exits at the cutting end via holes 41 formed in an otherwise continuous cutting element 42 (see also Figure 8). In order to facilitate registration of the holes 39 with the passages 38, such holes may be formed as slots. Alternatively or in addition, a circumferential groove may be formed in the flanged portion 27 of the adaptor, the passages 38 all terminating in such groove. In a variant, the inner tube 40 of the core drill 29 is made shorter than the outer tube and is arranged so that it terminates below the level of the ends of the passages 38 shown in Figures 7a and 7b. The cutting element 42 may for example consist of diamond dust or other hard material, for example cubic boron nitride or metal carbides or individually set diamonds in a sintered metal matrix formed in situ on the end of the tube. The holes 41 may be circular as shown or slots, or any other convenient shape. It will be appreciated that the adaptors described and illustrated in Figure 7a ond 7b may equally be used in conjunction with a drill formed in accordance with the description of any of Figures 1 to 6, and that any of the features of the drill described with reference to Figures 7a and 7b may be incorporated in the drill previously described with reference to Figures 5 and 6. Thus, in a particular example, a drill is provided with a plurality of cutting elements such as the elements 17 (Figures 5 and 6), and each of these elements has a number of cutting face discharge openings such as the openings 41 shown in Figure 8. In another modification, the spacers, e.g. the spacers 16 of Figure 5, are wider in proportion to the intervals between them, and in yet a further modification in cases where a number of discrete cutting elements is used, jets are provided between the cutting elements for the discharge of coolant in a direction substantially parallel with the axis of the drill. Finally, one or both tubes, preferably the inner tube alone, is slotted at the working end so that large particles of abraded material can be accumulated therein without damage to the drill. This feature is particularly advantageous for accommodating sections of steel rods cut away when drilling reinforced concrete, and it also provides reservoirs for coolant. WHAT WE CLAIM IS:

1. A core drill comprising a cutting head formed by at least one cutting element mounted on a tubular metal support

which support comprises at least one tube formed of at; least one rolled metal sheet and has a construction in which the tube wall is formed by at least two sheet-thicknesses and in which each end of said at least one sheet is secured lapwise to another metal sheet portion of the rolled tube to leave substantially cylindrically inner and outer faces.

2. A core drill according to Claim 1, characterised in that the or at least one said tube is formed by a single spirally rolled sheet of metal.

3. A core drill according to Claim 2, characterised in that there is a joggle in the medial portion of the sheet at the or each place where it passes over that end of the sheet which is on the inside of the tube and into which the other end of the sheet nests on the outside of the tube.

4. A core drill according to claim 1, characterised in that the or at least one said tube is formed from at least two cylindrical rolled sheets which nest one inside the other.

5. A core drill according to Claim 4, characterised in that the two ends of the outer sheet abut.

6. A core drill according to Claim 4 or 5, characterised in that the two ends of the inner sheet about.

7. A core drill according to any of claims 4 to 6, characterised in that the meeting ends of the separate rolled sheets are equally spaced about the periphery of the tube.

8. A core drill according ot any one of the preceding claims, characterised in that the free ends of the sheet metal from which a said tube is rolled are secured by spot welding.

9. A core drill according to any of the preceding claims, characterised in that said sheet metal is mild steel.

10. A core drill according to Claim 9, characterised in that said mild steel is galvanised.

11. A core drill according to Claim 2, characterised in that said support is a single spirally rolled tube and in that the cutting head is mounted on that end of the tube which will ensure that when the drill is rotated clockwise in use, the outer sheet end will trail.

12. A core drill according to any of claims 1 to 10, characterised in that said tubular support comprises inner and outer tubes (at least one of which is a rolled tube as specified in any of claims 1 to 10) held concentrically spaced apart by intervening spacer members and said cutting head defines one or more openings through which fluid introduced into the inter tube space can escape for cooling and/or lubicating the cutting head while the drill is in use.

13. A core drill according to Claim 12, characterised in that each said tube is formed of at least one rolled sheet.

14. A core drill according to Claim 12 or 13, characterised in that said outer tube is a spirally rolled tube and in that the cutting head is mounted on that end of that tube which will ensure that when the drill is rotated clockwise in use, the outer sheet end of said outer tube will trail.

15. A core drill according to any of claims 12 to 14, characterised in that said inner tube is a spirally rolled tube and in that the cutting head is mounted on that end of the tube which will ensure that when the drill is rotated clockwise in use, the inner sheet end of said inner tube will trail.

16. A core drill according to any of claims 12 to 15, characterised in that the space between the inner and outer tubes is between 2 and 5 mm across.

17. A core drill according to any preceding claim, characterised in that said cutting head comprises a plurality of said cutting elements which are circumferentially spaced apart to provide openings for the flow of coolant to the cutting surfaces.

18. A core drill according to any of claims 1 to 16 characterised in that there is a single cutting element defining said cutting head which is provided with channels defining openings for the flow of coolant to the cutting surface.

19. A core drill according to any one of the preceding claims, characterised in that the or each said cutting element consists of a sintered metal matrix holding an abrasive material.

20. A core drill according to Claim 19, characterised in that said abrasive material is selected from: diamond dust, cubic boron nitride, corundum, silicon carbide, metal carbides and/or individually set diamonds.

21. A core drill according to any one of the preceding claims, characterised in that the or each cutting element comprises one or more projections constituting a key engaging the support to prevent radial displacement.

22. A core drill according to any one of the preceding claims, characterised in that said support has one or more projections at its end which provide(s) a key engaging the or each cutting element against circumferential displacement.

23. A core drill substantially as herein described with reference to Figs. 1 and 2, Figs. 3 and 4, Figs. 5 and 6, and Figs. 7 and 8 of the accompaying drawings.

24. A core drill according to any of the preceding claims in combination with an adaptor, characterised in that said adaptor comprises a body portion adapted for connection to a drive motor and a flange por tion with a rebate defining a seat for the end of the tubular support of the core drill, at least one conically surfaced clamping member carried by screw means projecting through the flange pqrtion, and an expansible generally circular member seated on the or each conical member, the arrangement being such that when said screw means is tightened the or each such generally circular member rides up its associated conical surface and is forced to expand radially so that it will engage the interior of the tubular support of the core drill which is seated against said flange portion.

25. A core drill and adaptor according to Claim 24, characterised in that said core drill has a support comprising two tubes and in that said adaptor comprises at least one fluid passage communicating with the space between the tubes of said drill.

26. A core drill and adaptor according to Claim 24 or 25, characterised in that the or each said generally circular member is a coil spring.

27. A core drill and adaptor according to Claim 24 or 25, characterised in that the or each said generally circular member is a single-coil ring.

28. A core drill and adaptor according to Claim 27, characterised in that an additional such ring is used which is spaced from the first by a spacer ring, which additional single coil ring rides on a second conical surface.

29. A core drill and adaptor according to any of claims 24 to 28, characterised in that there is a single said conically surfaced clamping member carried by a plurality of bolts projecting through the flange portion.

30. A core drill and adaptor according to any of claims 24 to 28, characterised in that said screw means is constituted by a plurality of bolts projectiong through said flange and in that each such bolt carries a said conical member as a nut.

31. A core drill according to any of claims 1 to 23 provided with an adaptor, such adaptor being substantially as herein described with reference to Figure 7a or 7b of the accompanying drawings.