GB2031481A

GB2031481A - Drilling bits

Info

Publication number: GB2031481A
Application number: GB7838250A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-09-26
Filing date: 1978-09-26
Publication date: 1980-04-23
Also published as: GB2031481B

Abstract

A drill bit comprises a shank (Fig. 2) for rotation about an axis (3) and a cutting head (Fig. 1) secured to the shank (1) so as to be moveable with respect to the shank (1) between first and second positions, the diameter of the bit being greater when the cutting head is in its second position, this position being adopted during drilling. After it has been used to produce a hole which has been subsequently lined with a tubular casing, the bit can be removed from the hole without first having to remove the casing, reverse rotation causing the cutting head to adopt its first position. <IMAGE>

Description

SPECIFICATION Improvements in or relating to drill bits This invention relates to drill bits and more particularly but not exclusively is concerned with drill bits of the type suitable for drilling holes into the ground.

Drill bits form a hole having a diameter substantially equal to the outer diameter of the drill bit and, in conventional bits, this diameter is fixed. It is known when drilling holes in the ground to remove the bit and then line the hole with a tubular casing to prevent hole collapse. In order to be readily introducible into the hole the outer diameter of the tubular casing must, of necessity, be no greater than the diameter of the hole and hence the inner diameter of the casing must be somewhat less than the diameter of the hole. As a consequence, when a conventional drill bit is used it is not possible to extend the hole, once it has been lined, using the original drill bit since it will not pass through the casing and hence cannot be re-introduced into the hole.Thus, further drilling can only be continued using a drill bit having a diameter which is no greater than the inner diameter of the casing i.e. which is less than the diameter of the original bit. Thus, the diameter of the hole has to be gradually reduced. It is an object of the present invention to provide a drill bit which, after it has been used to produce a hole, can be re-inserted into the hole, even after the hole has been lined with a tubular casing, so as to enable the hole to be extended without any reduction in diameter.

It is also known, when drilling holes in the ground, to line the hole with a tubular casing without removing the drill bit from the hole by introducing the casing into the hole and causing it to follow the bit as it extends the hole.

As indicated above, the inner diameter of the casing must be somewhat less than the outer diameter of the drill bit and hence the drill bit cannot be extracted from the hole unless the casing is also removed from the hole.

It is an object of the present invention to provide a drill bit which, after it has been used to produce a hole which has been subsequently lined with a tubular casing, can be removed from the hole without first having to remove the casing.

According to the present invention there is provided a drill bit comprising a shank for rotation about an axis and a cutting head secured to the shank so as to be moveable with respect to the shank between first and second positions, the diameter of the bit being greater when the cutting head is in its second position than when the cutting head is in its first position.

In use, the drill bit of the present invention is suitably rotated about said axis with the cutting head in said second position so as to produce a hole having an internal diameter corresponding to the diameter of the bit when the cutting head is in its second position.

When it is desired to line the hole with a tubular casing, the bit can be extracted from the hole and a tubular casing be inserted into the hole. The tubular casing is such that its outer diameter is not greater than the diameter of the hole and its inner diameter is not less than the diameter of the bit when the cutting head is in its first position. Thereafter, the drill bit can be passed down the casing with the cutting head in its first position until the bottom of the hole is reached. Then, drilling may be recommenced with the cutting head in its second position so as to extend the hole without any reduction in diameter. Subsequently, the drilling bit may be removed from the hole by moving the cutting head to its first position with respect to the shank so that the bit can pass up the tubular casing.

Similarly, in the case where a tubular casing is inserted into the hole behind the bit, the bit can be readily withdrawn up the casing when its cutting head is in its first position with respect to the shank.

It is particularly preferred for the arrangement to be such that the cutting head automatically moves to its second postion as the bit is rotated in a first direction about said axis and for the cutting head to be automatically moved to its first position when the bit is rotated about the axis in an opposite direction.

In accordance with an embodiment, the cutting head is secured to the shank in a manner such that it can move between said first and second positions by executing a limited rotation with respect to the shank about a second axis which is parallel to but spaced from the axis of rotation of the shank.

The cutting head is thus mounted eccentrically with respect to the shank. In the case where the cutting head is rotatably mounted on the shank, the arrangement can be such that rotation of the shank about its axis in one direction causes the cutting head automatically to move to its second position and rotation of the shank about its axis in the opposite direction causes the cutting head automatically to move to its first position. The rotation of the cutting head with respect to the shank may be limited by abutments mounted on the shank and the cutting head in a manner such that they co-operate together, on the one hand, to prevent further rotation in one direction when the first position has been reached and, on the other hand, to prevent further rotation in the other direction when the second position has been reached.

In a preferred embodiment, one of the abutments is constituted by-first and second ends of a projecting shoulder having an inner cylindrical face extending between said first and second ends and the other of the abut ments is constituted by first and second flange portions of a collar having an outer cylindrical face extending between said first and second flange portions. In this way, relative rotation of the cutting head and the shank is allowed in one direction until the first end of the shoulder and the first flange portion engage together so as to define the first position and relative rotation of the cutting head and the shank is allowed in the other direction until the second end of the shoulder and the second flange portion engage together so as to define the second position.

It is particularly preferred to provide a means to prevent the debris produced during the drilling action from becoming lodged between the cutting head and the shank in a manner such as to prevent the cutting head moving between the first and second positions and, more particularly, moving from the second position to the first position. In the case of the embodiment above described, this may comprise an arrangement whereby a fluid such as air and/or water may be discharged from the collar at positions near to the first and second flange portions so as to blow, away from the vicinity of the flange portions, debris which could otherwise prevent the cutting head and shank adopting their first or second relative positions by stopping the ends of the shoulder from properly co-operating with the flange portions.Also, the distance between the inner cylindrical face of the shoulder and the outer cylindrical face of the collar should be kept to a minimum in order to minimise the tendency for debris to enter between the faces and possibly prevent the desired relative movement of the cutting head and the shank. Further, it is particularly preferred for the first end of the shoulder to be provided with a cutting edge to cut through any debris which may become affixed to the collar and obstruct the relative movement of the cutting head and the shank.

It is particularly preferred for the cutting head to include a generally cylindrical cutting portion which has an end formed as a cutting face and wherein the centre of the cylindrical cutting portion lies on a third axis which is parallel to but spaced from the second axis (i.e. the axis about which the cutting head has limited rotation with respect to the shank). In such a case, it is preferred for the third axis to be co-incident with said first axis (i.e. the axis of rotation of the shank) when the cutting head is in said first position. Moreover, in such a case, the diameter of the cylindrical cutting portion is preferably substantially the same as the diameter of the shank so that the diameter of the bit is substantially the same as the diameter of the shank when the cutting head is in its first position.

It is even more preferred for the cutting head to include an additional generally cylindrical cutting portion provided on the cutting face of said first-mentioned generally cylindrical cutting portion and having an end formed as an additional cutting face, wherein the centre of the additional generally cylindrical cutting portion lies on a fourth axis which Is parallel to but spaced from the third axis (i.e.

the axis of said first-mentioned cylindrical cutting portion). In such a case, it is preferred for said fourth axis to be co-incident with said first axis (i.e. the axis of rotation of the shank) when the cutting head is in its second position with respect to the shank.

For a better understanding of the invention and to show how the same may be carried into effect, reference may now be made, by way of example, to the accompanying drawing, in which: Figure 1 is a perspective view from the forward end and side of a cutting head of an under reaming drill bit in accordance with the present invention suitable for use with a hammer drill, Figure 2 is a perspective view from the forward end and side of the shank of the drill bit of Fig. 1, Figure 3 is a view of the forward end of the shank of Fig. 2 showing the cutting head of Fig. 1 in a first position with respect to the shank, and Figure 4 is a view of the forward end of the shank of Fig. 2 showing the cutting head of Fig. 1 in a second position with respect to the shank.

Referring to the drawings, and particularly to Fig. 2, the cutting head of the present invention comprises a generally cylindrical shank 1 provided with a coaxial shaft 2 and mounted for rotation about a longitudinally extending first axis 3. The outer peripheral surface of the shaft 2 carries splines 4 whereby it may be secured to a hammer drill in a manner such that the shank may be rotated about and reciprocated along the axis 3. A bore 5 is provided in the forward end face 6 of the shank 1. The bore 5 is generally cylindrical and the centre of the cylinder lies on an axis 7 which is parallel to, but spaced from, the axis 3 of rotation of the shank 1.

The bore 5 terminates within the shank 1 in a generally planar end face 8 provided with a central recess 9. A second bore 10 is provided and this extends from the end face 8 to the free end of the shaft 2. The bore 10 is coaxial with axis 3 and communicates, at the end face 8, with the recess 9.

The shank 1 also includes a lateral bore 11 extending from one side of the shank to the other. The bore 11 is at right angles to the bore 5 and intersects the bore 5 in the vicinity of its periphery.

A shoulder 1 2 is mounted on the forward end face 6. The shoulder 1 2 includes a first end 13, a second end 14 and an inner cylindrical face 1 5 extending between the ends 1 3 and 14. The first end 1 3 terminates in a cutting edge 41. The centre of curvature of the inner face 1 5 lies on axis 7. The ends 1 3 and 14 constitute abutments as will be described hereinafter.

Referring now to Fig. 1, the cutting head of the drill bit comprises a generally cylindrical stem 20 having its centre on an axis 21. The cutting head also includes a first generally cylindrical cutting portion 22 having its centre lying on an axis 23 which is parallel to, but spaced from, the stem axis 21. Thus, the first cutting portion 22 is eccentrically mounted on the stem 20. The cutting portion 22 has a generally circular end face 24 which carries a plurality of cutting teeth 25 formed of tungsten carbide so as to form a cutting face. The diameter of the first cutting portion 22 is substantially the same as the diameter of the cylindrical shank 1.

Provided on the end face 24 of the first cutting portion is a second generally cylindrical cutting portion 26. The centre of this second cutting portion 26 lies on an axis 27 which is parallel to, but spaced from, axes 23 and 21. The second cutting portion 26 has a generally circular end face 28 which also carries a plurality of cutting teeth 29 formed of tungsten carbide so as to form an additional cutting face.

The axis 7 of the bore 5 and the axis 3 of the shank 1 are spaced apart by a distance equal to the distance between the axis 23 of the cutting portion 22 and the axis 21 of the stem 20. This distance is also equal to the distance between the axis 27 of the cutting portion 26 and the axis of the stem 20.

That end of the first cutting portion 22 which is nearest to the stem 20 includes a part-cylindrical collar 30. The centre of curvature of the cylindrical collar 30 lies on the axis 21. The extremities of the collar 30 are defined by first and second upstanding flange portions 31 and 32. Flange portions 31 and 32 constitute abutments as will be described hereinafter. Flange portion 31 extends in a radial direction beyond the collar 30 by a relatively small amount whereas the flange portion 32 extends radially beyond the collar 30 by a relatively large amount so that the flange portion 32 is relatively more substantial and capable of withstanding much greater loads. An air gallery 33 is provided at each end of the collar 30 adjacent to the flange portions 31 and 32 and these galleries communicate with a central bore 34 provided in the stem 20.

The cylindrical surface of the first cutting portion 22 is fluted at three locations and a bore 35 is provided at the botton of each flute. Each of these bores 35 communicates with the bore 34 of the stem 20. The cylindrical surface of the second cutting portion 26 is also fluted in two places and at the bottom of each flute is provided a bore 36. The bores 36 also communicate with the bore 34 of the stem 20. The stem 20 also carries a pair of radial bores (only one of which can be seen in the drawing and is denoted by reference numeral 37) and these too are in communication with the bore 34 of the stem 20.

The stem 20 carries over a part of its circumference an arcuate slot 38 lying in a generally radial plane.

The drill bit is assembled by locating the stem 20 of the cutting head in the bore 5 of the shank 1 so that axes 7 and 21 are coincident. The cutting head is retained in the shank 1 by means of a pin (not shown) driven through the bore 11 of the shank 1 so as to lie in and extend through the arcuate slot 38 in the stem 20. In this way, the cutting head can rotate with respect to the shank about axis 7/21 through an angular displacement limited by the length of the arcuate slot 38.

The ends 1 3 and 14 of shoulder 1 2 and the flange portions 31 and 32 of the cutting head are appropriately dimensioned as to define the limits of the rotational movement of the cutting head about axis 7, 21 with respect to the shank 1. A first limit position is defined when the first end 1 3 of the shoulder 1 2 abuts against first flange portion 31 of the cutting head and a second limit position is defined when the second end 1 4 of the shoulder 1 3 abuts against the second flange portion 32 of the cutting head. The arrangement is such that when the cutting head moves from the first position (as shown in Fig.

4) the angular displacement a' effected (i.e.

the angle between an imaginary line extending from the second end 1 4 of shoulder 1 2 to the stem axis 21 and an imaginary line extending from the second flange portion 32 to the axis 21) is equal to the angle P (i.e. the angle between an imaginary line extending from the axis 23 of the first cutting portion 22 to the stem axis 21 and an imaginary line extending from the axis 27 of cutting portion 26 to the stem axis 21).Similarly when the cutting head moves from the second position (as shown in Fig. 4) to the first position (as shown in Fig. 3) the angular displacement (a") effected (i.e. the angle between an imaginary line extending from the first end 1 3 of the abutment shoulder 1 2 to the stem axis 21 and an imaginary line extending from the first flange portion 31 to the stem axis 21) is again equal to angle P.

The arrangement is thus such that when the cutting head is in its first position with respect to the shank (i.e. as shown in Fig. 3 where the position of the cutting head is shown in dotted lines superposed on the forward end face of the shank 1, the shaft 2 of shank 1 being shown in chain dotted line), the axis 23 of the cutting portion 22 is co-incident with axis 3 of the shank. Since the diameter of the cutting head is determined by the diameter of the cutting portion 22 and this is substantially the same as the diameter of the shank 1, the effective diameter of the drill bit is the diame ter of the shank 1 when the cutting head is in the first position.Now, when the cutting head moves to its second position with respect to the shank 1 (i.e. as shown in Fig. 4 where the position of the cutting head is shown in dotted lines superposed on the forward end face of the shank 1, the shaft 2 of the shank being shown in chain dotted lines), the axis 27 of the second cutting portion 26 is so coincident with the axis 3 of the shank and the cutting portion 22 is out of registry with the shank 1. Thus the effective diameter (40) of the drill bit is increased.

The radius of curvature of the inner cylindrical face 1 5 of the abutment shoulder 1 2 and the radius of curvature of the cylindrical face of the collar 30 should be selected such that the gap between these two surfaces is as small as possible in order to prevent debris from entering between the two surfaces and possibly stopping the cutting head and shank from moving between their first and second positions.

In use of the drill bit it is rotated and reciprocated about axis 3 in conventional manner and a fluid such as compressed air and/or water is passed into the drill bit via the bore 10, the recess 9, and bore 34 so as to be discharged from the cutting head via bores 35, 36 and 37 and galleries 33. The bit is rotated in an anti-clockwise direction as viewed from the forward end face and it is presented to the ground in which the hole is to be made. The resistance encountered by the cutting head when it contacts the ground tends to temporarily prevent the cutting head from rotating with the shank. As a consequence, the cutting head is automatically caused to adopt its second position with respect to the shank (see Fig. 4).Once this second position has been reached, the cutting head commences to rotate with the shank as a result of the thrust applied by the second end 14 of the shoulder 1 2 on the second flange portion 32 of the collar 30. Continued rotation of the drill bit in the same direction causes the cutting head to bore a hole having an effective diameter denoted by the line 40 in Fig. 4 i.e. a diameter somewhat greater than the diameter of the shank 1. The fluid emanating from the bores 35 and 36 and the air galleries 33 serves to remove debris from the vicinity of the cutting head. Once the desired depth has been reached, the rotation of the drill bit is stopped and reversed whilst fluid is continued to be passed through the bit.Because of the resistance of the cutting head to rotation, it tends not to rotate with shank 1 when the direction of rotation of the shank is reversed thus causing it automatically to adopt its first position with respect to the shank. Any debris which may be present on the collar 30 between the first end 1 3 and the first flange portion 31 which could prevent the end 1 3 and the first flange portion 31 from abutting together (and thus prevent the cutting head and shank adopting their first relative position) tends to be blown off the collar by the fluid emanating from the air galleries 33 and any residual debris is removed from the collar 30 by the cutting edge 41 on the first end 1 3. Thus, the cutting head can adopt its first position in which the diameter of the bit is essentially equal to the shank diameter. The drill bit can then be readily withdrawn from the hole. Thereafter the hole may be lined by inserting into it a tubular casing (not shown) having an outer diameter substantially equal to the maximum diameter of the hole (i.e. to the diameter 40 of the drill bit when the cutting head is in its second position) and having an inner diameter just slightly greater than the diameter of the drill bit when the cutting head is in its first position (i.e. slightly greater than the shank diameter). Once the hole has been lined, the same drill bit can be passed down the lined hole with the cutting head in its first position with respect to the shank until the end of the casing is reached.Rotation of the drill bit in the anticlockwise direction (as viewed from the cutting end) will then cause the cutting head automatically to adopt its second position thereby increasing the diameter of the drill bit as previously described. The hole can thus be extended without any reduction in diameter and the cycle can be repeated as often as desired.

In the event that the hole is lined by introducing the tubular casing into the hole behind the bit and allowing it to follow the bit down the hole, the bit can be withdrawn from the hole through the casing once the cutting head has been caused to adopt its first position with respect to the shank.

If desired, a plurality of cutting heads, as above described but of different diameters, may be provided, each head being capable of being secured to the shank 1 so that holes of different diameter can be formed merely by replacing one cutting head by another.

Claims

1. A drill bit comprising a shank for rotation about an axis and a cutting head secured to the shank so as to be moveable with respect to the shank between first and second positions, the diameter of the bit being greater when the cutting head is in its second position than when the cutting head is in its first position.

2. A drill bit as claimed in Claim 1 wherein the arrangement is such that the cutting head automatically moves to its second position as the bit is rotated in a first direction about said axis and to its first position when the bit is rotated about the axis in an opposite direction.

3. A drill bit as claimed in Claim 1 or 2 and including means to prevent debris pro duced during the drilling action from becoming lodged between the cutting head and the shank in a manner such as to prevent the cutting head moving from the second position to the first position.

4. A drill bit as claimed in Claim 1 or 2 and including means to prevent debris produced during the drilling action from becoming lodged between the cutting head and the shank in a manner such as to prevent the cutting head moving between the first and second positions.

5. A drill bit as claimed in any one of the preceding claims wherein the cutting head is secured to the shank in a manner such that it can move between said first and second positions by executing a limited rotation with respect to the shank about a second axis which is parallel to but spaced from the axis of rotation of the shank.

6. A drill bit as claimed in Claim 5 wherein the rotation of the cutting head with respect to the shank is limited by abutments mounted on the shank and the cutting head in a manner such that they co-operate together, on the one hand, to prevent further rotation in one direction when the first position has been reached and, on the other hand, to prevent further rotation in the other direction when the second position has been reached.

7. A drill bit as claimed in claim 6 wherein one of the abutments is constituted by first and second ends of a projecting shoulder having an inner cylindrical face extending between said first and second ends and the other of the abutments is constituted by first and second flange portions of a collar having an outer cylindrical face extending between said first and second flange portions whereby relative rotation of the cutting head and the shank is allowed in one direction until the first end of the shoulder and the first flange portion engage together so as to define the first position and relative rotation of the cutting head and the shank is allowed in the other direction until the second end of the shoulder and the second flange portion engage together so as to define the second position.

8. A drill bit as claimed in Claim 7 including an arrangement whereby a fluid may be discharged from the collar at positions near to the first and second flange portions so as to blow, away from the vicinity of the flange portions, debris which could otherwise prevent the cutting head and shank adopting their first of second relative positions by stopping the ends of the shoulder from properly co-operating with the flange portions.

9. A drill bit as claimed in Claim 7 or 8 wherein the distance between the inner cylindrical face of the shoulder and the outer cylindrical face of the collar is a minimum in order to minimise the tendency for debris to enter between the faces and possibly prevent the desired relative movement of the cutting head and the shank.

10. A drill bit as claimed in Claim 7, 8 or 9 wherein the first end of the shoulder is provided with a cutting edge to cut through any debris which may become affixed to the collar and obstruct the relative movement of the cutting head and the shank.

11. A drill bit as claimed in any one of Claims 5 to 10 wherein the cutting head includes a generally cylindrical cutting portion which has an end formed as a cutting face and wherein the centre of the cylindrical cutting portion lies on a third axis which is parallel to but spaced from the second axis.

12. A drill bit as claimed in Claim 11 wherein the third axis is co-incident with said first axis when the cutting head is in said first position.

1 3. A drill bit as claimed in Claim 1 2 wherein the diameter of the cylindrical cutting portion is substantially the same as the diameter of the shank so that the diameter of the bit is substantially the same as the diameter of the shank when the cutting head is in its first position.

14. A drill bit as claimed in Claim 11, 12 or 1 3 wherein the cutting head includes an additional generally cylindrical cutting portion provided on the cutting face of said firstmentioned generally cylindrical cutting portion and having an end formed as an additional cutting face, wherein the centre of the additional generally cylindrical cutting portion lies on a fourth axis which is parallel to but spaced from the third axis.

1 5. A drill bit as claimed in Claim 14 wherein said fourth axis is co-incident with said first axis when the cutting head is in its second position with respect to the shank.

1 6. A drill bit as claimed in Claim 1 substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.