GB2310623A

GB2310623A - Core drill

Info

Publication number: GB2310623A
Application number: GB9626081A
Authority: GB
Inventors: Anthony Roy Small; Ronald Peter Hill
Original assignee: Armeg Ltd
Current assignee: Armeg Ltd
Priority date: 1996-03-02
Filing date: 1996-12-16
Publication date: 1997-09-03
Anticipated expiration: 2016-12-16
Also published as: WO1997031743A1; GB9626081D0; GB2310623B; GB9604540D0

Abstract

A core drill 1 comprises a tubular body member 2, a plurality of cutting inserts 6 brazed to a leading end of the body member and a drive spigot 16 provided at the trailing end of the body member. The cutting inserts 6 are so profiled and fitted that point contact cutting is effected, with neutral rake. The inserts 6 are of hard metal with a thickness under 3 mm, typically 2 mm or less, and the wall thickness of the tubular body member 2 is <1.6 mm and preferably 1.2 mm or less. The core drill may be provided with a detachable closure plate 15 to facilitate core removal. Debris slots 8, 10 may also be provided.

Description

CORE DRILL This invention relates to a core drill, and particularly to a rotation only, i.e. non-hammer, core drill, adapted to be attached to a power tool, for the drilling for example, of masonry, brickwork, stonework, metals, timber, synthetic plastics materials etc.

A known diamond core drill comprises a hollow, thin-walled tube terminating at a leading end with a plurality of diamond particle inserts brazed in position, with a trailing end of the tube being closed off by a disc-like end plate which carries a drive spigot to be fitted into a chuck of a rotary drilling machine for instance, the tube being provided with a pair of diagonally opposed, inclined slots, for escape of dust and small debris/spoil, extending over substantially the full length of the tubular body member. Although quite capable of effecting core drilling, a practical difficulty with the above described drill, is the retention, within the body member, of a plug of the material being drilled and the presence of the end plate, which leads to troublesome time delay while the user attempts to remove the plug retained within the tube, e.g.

by inserting a screwdriver blade or other extraction tool through a slot to encourage discharge of the plug from the leading end of the tube, and frequently plus extraction requires hammering of the screwdriver or other extraction tool resulting in accidental damage to the relatively thin-walled tube. Typically, a plurality of equi-spaced diamond segments (typically 3mm or greater), have been employed in this known drill thickness requiring of course the removal of a minimum 3 mm annulus of the brick, stone, etc., being drilled.

A basic object of the present invention is to provide an improved core drill of the general type described above.

According to a first aspect of the invention, there is provided a rotation only core drill comprising a tubular body member, a plurality of cutting inserts brazed to a leading end of the body member and a drive spigot provided at the trailing end of the body member, wherein the cutting inserts are so profiled and fitted that point contact cutting is effected, with neutral rake, the inserts are of hard metal with a thickness under 3 mm, typically 2 mm or less, and the wall thickness of the tubular body member is reduced to < 1.6 mm and preferably 1.2 mm or less.

With prior art diamond core drills, the inserts cut by a grinding effect, with negative rake and with contact pressure over the entire length of the diamond inserts which is not only a limiting factor in speed of penetration, but also results in the disadvantageous generation of substantial heat, which disadvantages are largely obviated by the drill in accordance with the first aspect of the invention. Also, with prior art diamond inserts, these are unavailable under 3 mm thickness, due to manufacturing constraints. Consequently, drills incorporating such diamond inserts necessarily cut a minimum 3 mm kerf or annulus, and any reduction in wall thickness of the tubular body member provides no advantage and would merely reduce the mechanical strength of the body member.This last mentioned preferred feature. together with say 2 mm thick hard metal inserts, provides for increased speed of penetration. in contrast to prior art diamond core drills, and together with an externally hardened. tubular, body member permits, due to the strength increase of the latter, wall thickness reduction, so that a kerf or annulus of say 2 mm thickness is cut, compared to a kerf of at least 3 mm when using a conventional diamond core drill.

In accordance with another preferred feature the tubular body member is provided with a plurality of circumferentially spaced apart, relatively short length, debris exit slots, with a trailing end of one slot overlapping a leading end of an adjacent slot.

The slot arrangement of the drill in accordance with this last mentioned feature and, without the use of any dust extraction facilities, has been found in tests to promote far more effective debris exit from the interior of the body through the slots than the prior art construction.

However, as in most drilling conditions, plug formation will be encountered, and according to another aspect of the invention, of independent significance, there is provided a core drill comprising a tubular body member, a plurality of cutting inserts at a leading end of the body member and a drive spigot provided at the trailing end of the body member, wherein the trailing end of the body member is provided with a detachable closure plate.

Consequently, when a plug or core is retained within the body member, detachment of the closure plate results in a tubular body member that is open at both ends, so that the plug or core may be readily knocked out. Conveniently, detachment is effected by, e.g. a bayonet type fitting, an expanding mandrel, or a screw arrangement etc., between the closure plate and the trailing end of the body member.

Another practical difficulty encountered with prior art core drills results from the external scouring of, producing fine grooves in, the tubular body member that occurs in service, which scouring results in debris pick-up in the fine grooves, and the progressive build-up of debris particles which are difficult to remove as the temperatures generated in service encourage debris particle adherence to the extent that seize-up is not uncommon.

In accordance with another preferred feature the tubular body member is of externally surface hardened steel.

A core drill incorporating this last mentioned feature is thus resistant to extemal scouring, and accordingly is resistant to particle pick up as the spoil slides over the hardened external surface. Surface hardening also provides the additional advantage of strengthening the relatively weak, thin-walled tubular body member to further promote lengthened service life and resistance to abuse.

In accordance with another preferred feature, in which each cutting insert has a tapered profile matching a correspondingly tapered seat in the leading end of the body member to assist in frictional retention of the inserts prior to a securing step, e.g. brazing.

One example of core drill in accordance with various aspects of the invention, is shown in the accompanying drawings, in which: Figure 1 is a perspective view of the drill; Figure 2 is a side elevation of Figure 1; and Figure 3 is a view in the direction of arrow A of Figure 1.

In the drawings, a core drill 1 comprises a tubular body member 2 having a leading end 3 and a trailing end 4. The leading end 3 is provided with six axially extending tapered slots 5, each to receive a correspondingly profiled cutting insert 6 of hard material, e.g. tungsten carbide, such that the inserts are satisfactorily retained frictionally while brazing is effected. Each insert 6 projects beyond the leading end 3 to form a point contact cutting tooth 7, with neutral rake.

Behind the end 3, the body member 2 is provided with a plurality of circumferentially spaced-apart, relatively short length, debris exit slots 8, with trailing ends 9 of a first set of slots overlapping leading ends 10 of a second set of slots further from the leading end 3.

At the end 4, the body member 2 is provided with diametrically opposed bayonet slots 11 to receive retaining pins 12 of a relatively short length spigot portion 13 of an end cap 15 provided with an integral drive spigot 16 insertable in the chuck of a power tool for rotation only cutting.

he the inserts 6 are of hard metal they may be produced with a thickness of 2 mm or less, rather than the 3 mm or more that is unavoidable with diamond inserts. Consequently, only a 2 mm or less kerf is produced which, coupled with the point contact cutting by the teeth 7, in contrast to the grinding action of diamond inserts, a far more efficient cutting effect is produced.

Furthermore, the tubular body member 2 is of steel of 1.2 mm or less wall thickness and its exterior 17 is hardened or provided with a coating to prevent or minimise scouring in service, and attendant debris pick-up.

Finally, after completion of drilling, the masonry etc., core within the body member 2 may be readily removed by twisting the end cap 15 through a few degrees to permit withdrawal of the pins 12 from the bayonet slots 11, so that the plug may be knocked out of the open ended body member with minimum risk of inadvertent damage or deformation of the body member 2.

Claims

1. A rotation only core drill comprising a tubular body member, a plurality of cutting inserts brazed to a leading end of the body member and a drive spigot provided at the trailing end of the body member, wherein the cutting inserts are so profiled and fitted that point contact cutting is effected, with neutral rake; the inserts are of hard metal with a thickness under 3 mm typically 2 mm or less, and the wall thickness of the tubular body member is < 1.6 mm and preferably 1.2 mm or less.

2. A core drill as claimed in Claim 1, wherein the tubular body member is provided with a plurality of circumferentially spaced apart, relatively short length, debris exit slots, with a trailing end of one slot overlapping a leading end of an adjacent slot.

3. A core drill comprising a tubular body member, a plurality of cutting inserts at a leading end of the body member and a drive spigot provided at the trailing end of the body member, wherein the trailing end of the body member is provided with a detachable closure plate.

4. A core drill as claimed in Claim 3, wherein attachment and detachment of the closure plate is effected by, e.g. a bayonet type fitting, an expanding mandrel, or a screw arrangement etc., between the closure plate and the trailing end of the body member.

5. A core drill as claimed in any preceding Claim, wherein the tubular body member is of externally surface hardened steel.

6. A core drill as claimed in any preceding Claim, wherein each cutting insert has a tapered profile matching a correspondingly tapered seat in the leading end of the body member to assist in frictional retention of the inserts prior to a securing step, e.g. brazing.

7. A core drill substantially as hereinbefore described with reference to the accompanying drawings.