GB2312700A - Eccentric drill head detachably secured to drive means - Google Patents

Abstract

A drill for drilling and reaming a hole in the ground with the simultaneous placement of a casing tube 1 in the hole comprises, a drive means 2 with a stem 4 projecting from the front face thereof, a drill head 5 having a back face for abutting contact with the front face of the drive means 2, and having a support bore, the stem 4 fitting the bore with freedom for the drill head 5 to rotate relative to the drive means 2, at least one of the stem 4 and support bore having an axis offset from the axis of the respective drive means 2 and drill head 5, there being a means 8,9,10 to limit the degree of relative rotation between the drill head and the drive means and there being means to detachably secure the drill head 5 on the stem 4 and prevent relative axial movement, said means preferably being ball bearings fed through a hole 11 in the wall of the head 5, to be positioned in the cooperating recess, the opening 11 being closed by a threaded stud.

Description

DRILL MEANS This invention relates to drill means and is particularly concerned with a drill means adapted to drill and ream a hole in the ground in advance of a trailing casing tube.

To enable the drilling of a hole to take a casing tube, it is necessary that the periphery of a drill means is at a radius greater than the radius of the casing. As at the end of the drilling operation, the drill means must be removed up through the casing that has been positioned in the drilled hole, the drill means must be capable of a radial displacement in the transverse plane from a first position where a hole at the outer diameter of the casing can be drilled to a position where the drill means is within the inner diameter of the casing and when the drill means can be withdrawn through the casing.

There are several constructions known hitherto whereby this objective can be achieved, such as, for example, as disclosed in US Patent 3848683 and in a commercially available drilling system known as the BULROC (RTM) overburden drilling system. Whilst these systems constitute a different approach to the requirement of the drilling of an oversize hole and the subsequent withdrawal of the drill through a casing tube, they have the similarity in the provision on the drill head of a complex stem with a coarse pitch helical screw to enable a relative rotation of the drill head or a reaming attachment on the drill head, about a drive means to which the drill head is secured, first to bring the drill head/reaming attachment to an eccentric position to allow the drilling of an oversize hole and then to bring the drill head/reaming attachment to within the inner diameter of the casing to permit its withdrawal.

Whilst such systems are effective, they are relatively complex and relatively expensive, and any wear on the drill head/reaming attachment results in the need to discard, or scrap, the entire drill head and stem.

The object of the present invention is to provide a drill means, no less effective than any prior construction in allowing the drilling of an oversize hole to permit the location of a trailing casing and the subsequent extraction of the drill means through the casing, but at considerably less expense than has hitherto been possible.

According to the present invention, a drill means comprises a drive means with a step projecting from the front face thereof, a drill head having a back face for abutting contact with the front face of the drive means, and having a support bore, the stem fitting the bore with freedom for the drill head to rotate relative to the drive means, at least one of the stem and support bore having an axis offset from the axis of the respective drive means and drill head, there being a means to detachably secure the drill head on the stem and prevent relative axial movement, and there being a means to limit the degree of relative rotation as between the drill head and the drive means. Preferably, both the stem and the bore have axes offset from the respective axis of the drive means and the drill head.

To locate the drill head on the stem of the drive means, it is preferred to provide a circumferential recess in the wall of the bore of the drill head and a matching part-circumferential recess in the periphery of the stem, ballbearing means being located in the co-operating recesses to lock the drill head against axial movement with respect to the stem and hence drive means, and at the same time facilitate the relative rotation of the drill head on the stem. To enable the fitting of the ballbearing means, the drill head may have a radial hole emerging in its circumferential recess such that with the drill head located on the stem and with the radial hole aligned with the recess on the stem ballbearings can be introduced through the hole to position them in the co-operating recesses. The radial hole can subsequently be closed by an appropriate plug.

To restrict the degree of relative rotation permitted as between the drill head and the drive means, the bore in the drill head may have a counterbore extending around marginally more than 1800 of its circumference, and the stem may have an axial, part-circular recess in its periphery with a pin to engage in the part-circular recess. With the drill head fitted to the stem the pin locates in the part- circumferential counterbore to permit a 1800 rotation between the drill head and the drive means.

The offset relationship between the axis of the stem or the bore of the drive means and drill head respectively, is such that with the drill head brought into ground contact, the percussive rotary drive imparted to the drill head by the drive means and the friction effect as between the drill head and the ground is such that at start-up a 1800 rotation between the drill head and the drive means is caused, the further percussive rotary drive imparted to the drill maintaining the drill in an offset condition to drill a hole of larger diameter than the drill head itself and to permit a trailing casing to be drawn into the hole as it is drilled. By having both of the stem and the bore offset, the relative rotation between the drill head and the drive means is even more pronounced to allow an even larger hole to be drilled. At the cessation of drilling a reverse rotation induced in the drive means causes a relative rotation between the drive means and the drill head, with the pin moving around the circumferential counterbore to the opposite extremity, to swing the drill head to a position where it is aligned with the drive rneans and hence within the diameter of the trailing casing, and when the drill head along with the drive means can be withdrawn up the casing.

When extracted from the hole, and in extremely simple manner, the plug closing the radial hole in the drill head can be removed, the ballbearings extracted from the co- operating recesses, and the drill head slipped from the stem. The drill head alone can then be replaced if badly wom. Similarly, inspection can be made of the pin and if it is worn, it can be removed and replaced.

The cost of a replacement drill head of the invention is noticeably less than conventional drill heads by the avoidance of the provision of an integral stem, particularly one with a coarse helical thread, as has been mentioned earlier in relation to prior art, and if the head does then need to be replaced it can be effected at much less cost than hitherto. With the drive connection between the drive means and the drill head being a simple pin, it can be inspected when the drive head has been removed and if wom, replaced at very low cost. The prospect of damage to the ballbearings is minimal given that there is no axial movement permitted as between the drill head and the drive means, the structure being such that the front face of the drive means is in intimate contact with the back face of the drill head.

The advantages that are therefore achieved by the invention are reduced manufacturing cost, reduced dismantling and assembly costs, and hence reduced refurbishment costs, by a construction that does not detract from the ability for the drill head to be rotated eccentrically on the drive means to provide a so-called overburden drive system.

One embodiment of the invention is illustrated in the accompanying drawing which is an exploded, perspective view of a drill means in accordance with the invention.

One embodiment will now be described with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a drill head and drive means in accordance with the invention; and Figure 2 is a plan view of the drill head of Figure 1.

In the drawings a casing for lining a drilled hole is indicated at 1, and lying within the casing is a drive means 2 with a splined shaft 3 for connection to the end of a hammer (not shown) at the end of a drill string (not shown) extending down the casing. The association between the hammer and drive means and the casing and whereby the casing can be carried down the drilled hole is relatively conventional and requires no description here.

As has been discussed above, to enable a casing to be drawn down a drilled hole during drilling, the drill head must be able to drill a hole at a diameter of the outside diameter of the casing, but, at the end of the drilling operation, to enable the drill head to be withdrawn through the casing, it must have a diameter less than that of the inner diameter of the casing.

In accordance with the invention and to achieve this, a stem 4 is provided on the front face of the drive means 2, the axis of which is offset in relation to the axis of the drive means, and the drill head 5 has a support bore 6 extending along the head from its back face, the axis of the support bore being offset from the axis of the drill head. Thus, with the drill head located on the stem, it can be rotated from a position where it has a part of its periphery extending to beyond the outside diameter of the casing, to a position where it is aligned with the drive means. In the first condition, a hole of a diameter to receive the casing can be drilled, and in its second position, the drill head along with the drive means and its hammer, can be withdrawn through the casing as the drill string is withdrawn, to leave the casing in situ.

It is highly advisable to limit the extent to which the drill head can rotate on the stem, and also ensure that the required rotation can be achieved relatively effortlessly.

To limit the degree of rotation, the support bore is provided with an arcuate recess 7 extending along part of its length from its back face, and the stem 4 has a semicircular recess 8, there being a pin 9 that locates in the recess 8, arcuate recess 7, the clockwise and anti-clockwise rotation of the head 5 on the stem 4 being limited by the pin 9 being brought into contact with one end or the other of the arcuate recess 7. To ensure the absence of a relative axial movement of the drill head on the stem and ensure freedom of rotation of the head 5 between its limiting positions, a further recess 10 is provided around a part of the periphery of the stem 4, to cooperate with a matching recess in the wall of the support bore 7, and with the head 5 fitted to the stem 4, ball bearings can be fed through an opening 11 through the wall of the head, to be positioned in the co-operating recesses, the opening being closed by a threaded stud.

Thus, at the onset of the drilling, the head 5, on its hammer, and attached to the first length in the drill string, is inserted through a first length of casing, and the front face of the head, bearing button bits 12 is brought into ground contact. Rotation of the drill string and the frictional contact of the head with the ground causes a relative rotation of the head 5 on the stem 4 of the drive means 2, to cause the head to assume an eccentric position and put the face 13 with its button bits and the face 14 and its button bits in a position where further rotation of the drill string causes a rotation of the drill head which, in conjunction with the hammering of the drill head into the ground causes the boring of a hole of a diameter to enable the casing 1 to be carried down the hole with the drill head, drive means and hammer.

At the end of the drilling operation, the drill string and hence drive means is caused to rotate in the opposite direction, to cause an opposite relative rotation between the stem 4 and the head 5, to bring the pin to the opposite extremity of the recess 7, further rotation in the same direction causing the drill head to rotate on the stem which, consequent on the offset positions of the stem 4 and support bore 6 axis brings the head into register with the drive means 2, and hence within the inner diameter of the casing, to enable the drill head to be withdrawn with the drill string through the casing.

Claims (7)

1. A drill means comprises a drive means with a stem projecting from the front face thereof, a drill head having a back face for abutting contact with the front face of the drive means, and having a support bore, the stem fitting the bore with freedom for the drill head to rotate relative to the drive means, at least one of the stem and support bore having an axis offset from the axis of the respective drive means and drill head, there being a means to detachably secure the drill head on the stem and prevent relative axial movement, and there being a means to limit the degree of relative rotation as between the drill head and the drive means.

2. A drill means as in Claim 1, wherein both the stem and the bore have axes offset from the respective axis of the drive means and the drill head.

3. A drill means as in Claim 1 or Claim 2, wherein to locate the drill head on the stem of the drive means, a circumferential recess is provided in the wall of the bore of the drill head and a matching part-circumferential recess in the periphery of the stem, ballbearing means being located in the co-operating recesses to lock the drill head against axial movement with respect to the stem and hence drive means, and at the same time facilitate the relative rotation of the drill head on the stem.

4. A drill means as in Claim 3, wherein to enable the fitting of the ballbearing means, the drill head is a radial hole emerging in its circumferential recess such as that with the drill head located on the stem and with the radial hole aligned with the recess on the stem ballbearings can be introduced through the hole to position them in the co-operating recesses.

5. A drill means as in Claim 4, wherein the radial hole is closed by an appropriate plug.

6. A drill means as in any of Claims 1 to 5, wherein to restrict the degree of relative rotation permitted as between the drill head and the drive means, the bore in the drill head has a counterbore extending around marginally more than 1800 of its circumference, and the stem may have an axial, part-circular recess in its periphery with a pin to engage in the part-circular recess, whereby with the drill head fitted to the stem the pin in the part-circular recess locates in the part circumferential counterbore to permit a 1800 rotation between the drill head and the drive means.

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