GB2193677A

GB2193677A - Core drill bit

Info

Publication number: GB2193677A
Application number: GB08715634A
Authority: GB
Inventors: William George Michael Strong; Richard Andrew Richman
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-07-12
Filing date: 1987-07-03
Publication date: 1988-02-17
Also published as: GB8715634D0

Abstract

A core drill bit has a cylindrical body part adapted to be held at one end in the throat of a rotary percussion drill. The body part of the bit is formed adjacent the free end surface 21 with chordal passages 27. Circumferentially distributed slots 19 respectively transect the passages 27. The walls of the chordal passage portion 27b extending from the trailing wall portions of the several said slots 19 are each internally threaded. Cutter tips 23 each have an aperture as 25 extending therethrough and communicating between the chordal passage portions 27a and 27b. The cutter tips 23 are each releasably secured with respect to the body part by threaded male fastener elements 29 which enter the apertures 25 and engage the threaded internal wall portions of the passages 27b. The heads 31 abutment portions 31 (Fig. 3) or 29a (Figs. 7,8) bear against the cutter tips 23 under screw tension. <IMAGE>

Description

SPECIFICATION Core drill bit This invention relates to core drill bits which have a generally cylindrical body part adapted at one end to be engaged by or to engage an output member of a drill, such, for example, as a percussion drill, and, at the other end, a multiplicity of circumferentially distributed slots leading from the free end surface thereof and a corresponding multiplicity of cutter tips respectively fixed within the said slots. Core drill bits as specified above are herein referred to as core drill bits "of the kind described". Core drill bits are employed in drilling through brick work and similiar structural ceramic material; they are not useful for the purposes of drilling through e.g. metals.

According to the invention, the body part of a core drill bit of the kind described is formed adjacent the said free end surface with chordally extending passages; the circumferentially distributed slots respectively intercept the said chordal passages; the several cutter tips each have a recess therein extending in the direction of rotation of the drill bit and communicating with the chordally extending passages leading from the cutter tip receiving slots; and the several cutter tips are releasibly secured with respect to the body part by means of individual male fastener elements which respectively extend into the recesses in the cutter tips and which are adapted respectively positively to engage the walls of the said passages the said fastener elements having abutment means respectively bearing against the said cutter tips under the strain induced in the fastener elements by their positive engagement with the said passage walls.

In one hereinafter described embodiment, the circumferentially distributed slots respectively transect the said chordally extending passages; the walls of the chordal passage portions extending from the trailing walls (in relation to the drill bit sense of rotation) of the several said slots are each internally threaded; the recesses in the several cutter tips are apertures communicating between the chordal passage portions leading from each side of the cutter tip receiving slots; and the male fastener elements are threaded elements respectively extending through the said apertures through the cutter tips and respectively engaging, by screw action the internally threaded trailing passage walls, the said abutment means being respectively constituted by the heads of the several male fastener elements and which, under the tensile loads induced in the male fastener elements by the screw action as aforesaid, bear against the leading major surfaces of the cutter tips.

In another hereinafter described embodiment, threaded chordal passages respectively extend from the leading edges of the circumferentially distributed slots; the several male fastener elements each have a threaded main body portion, at one end a spigot portion, and between the main body and spigot portions the abutment means; the main body portions of the several male fastener elements being screwed respectively into the said leading edge chordal passages so that, with the spigot portions respectively received within the recesses of the several cutter tips, the abutment means respectively bear against the cutter tips under the compressive loads induced, by the screw action, in the fastener elements.

The several male fastener elements may each comprise an elongate member an end face of which is formed with an axially extending recess the internal wall of which is adapted to be engaged by a torque rod, such for example as an Allen key or a splined screwdriver bit, of complementary shape.

Alternatively, or additionally, the end face of the threaded male fastener element remote from the first mentioned end face may also be formed with an axially extending recess adapted to be engaged by a torque rod as aforesaid and by which the said fastener may be driven.

Core drill bits in accordance with the invention permit the ready removal of the cutter tips without the need to engage the services of a specialist. Damaged or worn tips may be restored to their desired user condition; and pending such renewal or repair spare tips may be secured in the core drill bit. The core drill bit is therefore of particular benefit for small tool hire and like business entities.

Two embodiments of the invention are hereinafter described with reference to the accompnying drawings, in which: Figs. 1 and 2 are elevational and plan views, respectively, of one embodiment; Fig. 3 shows a section taken on Ill-Ill of Fig 1; Fig. 4 shows composite sections showing, further, the manner in which, in the embodiment, the cutter tips are secured.

Figs. 5 and 6 are elevational and plan views, respectively, of the second core drill embodiment; Fig. 7 shows a section taken on VIl-VIl of Fig. 5; and Fig. 8 shows composite sections corresponding in respect of the second embodiment to the sections of Fig. 4.

In the ensuing description of the two embodiments corresponding parts of the core drill bear the same reference numerals.

The core drill bit 11 for piercing refractory bodies, as masonry, has a generally cylindrical body part 13 adapted at the end 15 to receive an output member (not shown) of a drill, more particularly, a rotary percussion drill.

The core drill bit, being of the kind described, the other end 17 of the bit 11 has a multiplicity of circumferentially distributed slots, as 19, leading from the free end surface 21 of the body 13. Within each slot there is a cutter tip 23 of e.g. tungsten carbide.

Referring, specifically, to the embodiment of Figs. 1 to 4 the body part 13 is formed adjacent the free end surface 21 with chordal passages 27. The circumferentially distributed slots 19 respectively transect the said chordal passages 27. The walls of the chordal passage portion 27b extending from the trailing walls (in relation to the drill bit sense of rotation) of the several said slots 19 are each internally threaded. The cutter tips 23 each have an aperture, as 25, extending therethrough in the direction of rotation R of the drill bit, and communicating between the chordal passage portions 27a and 27b extending from the leading and trailing walls of the cutter tip receiving slots 19.The several cutter tips 23 are releasibly secured with respect to the body part 13 by means of threaded male fastener headed elements 29 which extend through the apertures 25 and engage the threaded internal wall portions of the passages 27b. The chordal passage portions 27a are of a greater diameter than the passage portions 27b; and the heads 31 of the elements 29 are received within the larger diameter passage portions 27a and abut and bear against the leading major surface of the cutter tips 23 under screw tension.

The heads 31 of the elements 29 each have an axially extending recess 33 shaped to receive an Allen key or, more desirably, are internally splined to receive a complementarily splined torque member (not shown). The ends 35 of the fastener elements 29 remote from the heads 31 may also have an axially extending recess, again shaped to receive an Allen key or a splined torque member. The elements 29 (and, hence, the cutter tips 23) may be readily removed to permit the drill bit to be maintained in a serviceable condition.

In the embodiment of Figs. 5 to 8 the chordal passages 27 extend only from the leading edges of the slots 19 and are threaded. The several cutter tips 23 are releasibly secured with respect to the body part 13 by means of male fastener elements 29 each having a threaded main body portion 29b and, at one end, a spigot portion 29s, and between the spigot portion 29s and the body portion 29b abutment means 29a. The main body portion 29b of the elements 29 are screwed, respectively, into the threaded passages 27 so that, with the spigot portions 29s respectively received within the recesses 25 of the cutter tips 23 the abutment means 29a bear, respectively, against the cutter tips 23 under the compressive loads induced, by the screw action, in the fastener elements 29.

As with the first embodiment the free ends of the male fastener elements 29 have axially extending recesses adapted to be engaged by a torque rod-an Allen Key or splined screwdriver bit-of complementary shape.

Claims

1. A core drill bit of the kind described in which the said body part is formed adjacent the said free end surface with chordally extending passages; the circumferentially distributed slots respectively intercept the said chordal passages; the several cutter tips each have a recess therein extending in the direction of rotation of the drill bit and communicating with the chordally extending passages leading from the cutter tip receiving slots; and the several cutter tips are releasibly secured with respect to the body part by means of individual male fastener elements which respectively extend into the recesses in the cutter tips and which are adapted respectively positively to engage the walls of the said passages the said fastener elements having abutment means respectively bearing against the said cutter tips under the strain induced in the fastener elements by their positive engagement with the said passage walls.

2. A core drill bit as claimed in claim 1 in which the circumferentially distributed slots respectively transect the said chordally extending passages; the walls of the chordal passage portions extending from the trailing walls (in relation to the drill bit sense of rotation) of the several said slots are each internally threaded; the recesses in the several cutter tips are apertures communicating between the chordal passage portions leading from each side of the cutter tip receiving slots; and the male fastener elements are threaded elements respectively extending through the said apertures through the cutter tips and respectively engaging, by screw action the internally threaded trailing passage walls, the said abutment means being respectively constituted by the heads of the several male fastener elements and which, under the tensile loads induced in the male fastener elements by the screw action as aforesaid, bear against the leading major surfaces of the cutter tips.

3. A core drill bit as claimed in claim 1 in which the threaded chordal passages respectively extend from the leading edges of the circumferentially distributed slots; the several male fastener elements each have a threaded main body portion, at one end a spigot portion, and between the main body and spigot portions the abutment means; the main body portions of the several male fastener elements being screwed respectively into the said leading edge chordal passages so that, with the spigot portions respectively received within the recesses of the several cutter tips, the abutment means respectively bear against the cutter tips under the compressive loads induced, by the screw action, in the fastener elements.

4. A core drill bit as claimed in any preceding claim in which the several male fastener elements each comprise an elongate member an end face of which is formed with an axially extending recess the internal wall of which is adapted to be engaged by a torque rod, such for example as an Allen key or a splined screwdriver bit, of complementary shape.

5. A core drill bit as claimed in claim 4 in which the end face of the threaded male fastener element remote from the first mentioned end face may also be formed with an axially extending recess adapted to be engaged by a torque rod as aforesaid and by which the said fastener may be driven.

6. A core drill bit substantially as hereinbefore described with reference to Figs. 1 to 4 or Figs. 5 to 8 of the accompanying drawings.