DRILLING APPARATUS
United States Patent 3758059
A drilling machine assembly is movable on a base between a drilling position and a hoisting position by operation of power means such as a hydraulic cylinder unit. The drilling machine assembly can be held firmly in each of the two positions by the interengagement of wedging surfaces on the machine assembly and on the base with the power means operating, thereby eliminating the need to operate screw clamps for this purpose.
US Patent References:
A WALKING PLATFORM FOR DRILLING EQUIPMENT WITH MEANS FOR OSCILLATING THE DRILL TUBE
Reimann - July 1971 - 3595322
Foot rest
Santaniello - November 1922 - 1435744
/1204544.html
Caverno - November 1916 - 1204544
COMBINED EARTH BORING AND POST DRIVING APPARATUS
Lisenby - July 1969 - 3576218
A WALKING PLATFORM FOR DRILLING EQUIPMENT WITH MEANS FOR OSCILLATING THE DRILL TUBE
Reimann - July 1971 - 3595322
Foot rest
Santaniello - November 1922 - 1435744
/1204544.html
Caverno - November 1916 - 1204544
COMBINED EARTH BORING AND POST DRIVING APPARATUS
Lisenby - July 1969 - 3576218
Application Number:
05/187011
Publication Date:
09/11/1973
Filing Date:
10/06/1971
View Patent Images:
Export Citation:
Assignee:
Mindrill Limited (Victoria, AU)
Primary Class:
Other Classes:
248/668, 248/658, 173/191
International Classes:
E21B7/02; E21B15/00; E21B3/02
Field of Search:
248/23,298 173/44,43 175/220 299/31
Primary Examiner:
Foss, Franklin J.
Claims:
I claim
1. Drilling apparatus comprising, in combination, a base; rail means mounted on said base to extend longitudinally in one general direction; a drilling machine assembly supported on said rail means for movement in said general direction back and forth between a drilling position and a hoisting position; said drilling machine assembly including a drilling head operable, when said assembly is in the drilling position, to grip and rotate an upright drill rod; pressure fluid cylinder means actuable to move said drilling machine assembly between its drilling and hoisting positions; an upright mast having its lower end pivotally connected to said drilling machine assembly; mast support means pivotally connected to the upper end of said mast; first and second wedging surface means on said rail means; and first and second wedging surface means on said drilling machine assembly; said first wedging surface means on said rail means and said first wedging surface means on said drilling machine assembly interengaging responsive to movement of said drilling machine assembly to its drilling position by actuation of said pressure fluid cylinder means to provide, in conjunction with the actuated pressure fluid cylinder means, locking of said drilling machine in its drilling position; said second wedging surface means on said rail means and said second wedging surface means on said drilling machine assembly interengaging, upon movement of said drilling machine assembly to its hoisting position by reverse actuation of said pressure fluid cylinder means to provide, in conjunction with the actuated pressure fluid cylinder means, locking of said drilling machine assembly in its hoisting position.
2. Drilling apparatus as claimed in claim 1, wherein the pressure fluid cylinder means is a double acting fluid cylinder unit connected between the drilling machine assembly and the base.
3. Drilling apparatus, as claimed in claim 1, in which said rail means comprises plural rails extending longitudinally in said one general direction; said drilling machine assembly including support collars slidable along said rails; said first and second wedging surface means on said rail means being formed by first and second external surfaces tapered conically in respective opposite directions longitudinally of said rails; said first and second wedging surface means on said drilling machine assembly being formed by first and second internal, conically tapered end surfaces of said collars.
4. Drilling apparatus, as claimed in claim 1, in which said first and second external, conically tapered surfaces are the surfaces of conically tapered rail end pieces positioned at opposite ends of said rails.
1. Drilling apparatus comprising, in combination, a base; rail means mounted on said base to extend longitudinally in one general direction; a drilling machine assembly supported on said rail means for movement in said general direction back and forth between a drilling position and a hoisting position; said drilling machine assembly including a drilling head operable, when said assembly is in the drilling position, to grip and rotate an upright drill rod; pressure fluid cylinder means actuable to move said drilling machine assembly between its drilling and hoisting positions; an upright mast having its lower end pivotally connected to said drilling machine assembly; mast support means pivotally connected to the upper end of said mast; first and second wedging surface means on said rail means; and first and second wedging surface means on said drilling machine assembly; said first wedging surface means on said rail means and said first wedging surface means on said drilling machine assembly interengaging responsive to movement of said drilling machine assembly to its drilling position by actuation of said pressure fluid cylinder means to provide, in conjunction with the actuated pressure fluid cylinder means, locking of said drilling machine in its drilling position; said second wedging surface means on said rail means and said second wedging surface means on said drilling machine assembly interengaging, upon movement of said drilling machine assembly to its hoisting position by reverse actuation of said pressure fluid cylinder means to provide, in conjunction with the actuated pressure fluid cylinder means, locking of said drilling machine assembly in its hoisting position.
2. Drilling apparatus as claimed in claim 1, wherein the pressure fluid cylinder means is a double acting fluid cylinder unit connected between the drilling machine assembly and the base.
3. Drilling apparatus, as claimed in claim 1, in which said rail means comprises plural rails extending longitudinally in said one general direction; said drilling machine assembly including support collars slidable along said rails; said first and second wedging surface means on said rail means being formed by first and second external surfaces tapered conically in respective opposite directions longitudinally of said rails; said first and second wedging surface means on said drilling machine assembly being formed by first and second internal, conically tapered end surfaces of said collars.
4. Drilling apparatus, as claimed in claim 1, in which said first and second external, conically tapered surfaces are the surfaces of conically tapered rail end pieces positioned at opposite ends of said rails.
Description:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to drilling apparatus and particularly to core drilling apparatus used in exploratory drilling.
2. Description of Prior Art
The invention has particular but not exclusive application to small drilling rigs and is concerned with rigs of the type having a drilling machine which can be moved back and forth between a forward drilling position and a rearward hoisting position. In apparatus of this type the drilling machine assembly generally comprises a drive motor which drives a hoist drum at the rear of the assembly and a drilling head at the front of the assembly. During drilling the machine assembly is located in its forward position and the drilling head is then located directly over the hole being drilled. The drilling head grips and rotates the drill string which extends downwardly through it and the drill rod is supported by a hoisting rope passed over one or more sheaves at the top of the mast of the rig and then down to the hoist drum. When the drill string is to be retrieved from the hole, the whole drilling machine assembly is drawn or "racked" back to its rearward position and the drill string is hoisted directly by the hoist rope past the retracted drilling head.
For both the drilling and hoisting operations the drilling machine must be firmly locked in position and it is usual to provide a number of clamping bolts for this purpose. The necessity to release and reclamp these bolts when the drilling machine assembly is to be moved has proved to be most troublesome. A much more convenient arrangement is provided by the present invention.
SUMMARY OF THE INVENTION
The invention provides drilling apparatus of the type wherein a drilling machine assembly is movable on a base between a drilling position and a hoisting position by operation of power means and characterised in that the drilling machine assembly can be held in each of said positions by the interengagement of wedging surfaces on the machine assembly and on the base with the power means operating.
The machine assembly may be supported on a plurality of collars encompassing and slidable along respective rails on the base and the interengaging wedging surfaces may be provided at the ends of the collars and at the ends of the rails. For example, the rails can be cylindrical and the collars annular and there may be conically tapered end pieces at the ends of the rails to engage conically tapered internal surfaces of the collars.
In order that the invention may be more fully explained, one particular embodiment will now be described in some detail with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings,
FIG. 1 is a side elevation of a drilling apparatus shown in condition for drilling operations;
FIG. 2 is a side elevation of the apparatus in condition for hoisting operations;
FIG. 3 is an enlarged cross-section generally on the line 3--3 in FIG. 1;
FIG. 4 is an enlarged and part broken view of the bottom part of the apparatus when in the condition of FIG. 1; and
FIG. 5 is a view similar to that of FIG. 4 but with the apparatus in the condition of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The illustrated apparatus comprises a drilling machine assembly denoted generally as 11 and mounted on a fixed base 12 in a manner to be described below. The machine assembly 11 is of conventional construction comprising a drive motor 13 which drives a hoist 14 and a drilling head 16. An upright mast 17 is pivotally connected at its lower end to the machine assembly 11 by a pivot connection 18. For the most part mast 17 is of light-weight box girder construction comprising longitudinal stringers 19 and lattice bracing members 21, but its lower end is formed by a bracket 22 connected to the machine assembly 11 by a pivot pin forming the pivot connection 18 about an axis 24.
The upper part of mast 17 is pivotally connected at 26 to the upper end of a stay arm 27 which is inclined at an acute angle to the mast and is pivotally connected at its bottom end to an anchor 29 by a pivot connection 28. Anchor 29 is carried by a mount 31 which is fixed relative to the machine base 12 either by being connected directly to it or by being set firmly in the ground. Arm 27 comprises a central girder section 32, a bottom adjustment portion 33 and an upper portion 34. The lower adjustment portion 33 comprises a screw threaded stem 36 clamped to the bottom of the arm portion 32 by lock nuts 37 and screw-fitted into an internal thread socket member 38 which is connected to the anchor 29 by a ball joint forming the pivot connection 28.
The upper part 34 of arm 27 is bifurcated so as to have two end portions 41 extending one to either side of the upper part of the mast and pivotally connected at their upper ends to the mast by a composite pivot pin 42. The composite pivot pin comprises a central tube 43 to which the upper ends of the arm parts 41 are clamped by studs 44. Pivot tube 43 extends through a bearing tube 46 which is fixed between side plates 47 on the upper part of the mast. Thus the mast 17 and stay arm 27 can pivot relative to one another about the axis 48 of the pivot and bearing tubes 43,46.
A cradle 49 carrying a pair of head sheaves 50, 51 hangs from the pivot bearing tube 46 at the upper end of the mast. The cradle 49 comprises a frame 52 in which the sheaves 50, 51 are journalled and a pair of yoke members 53. The yoke members are of generally inverted U-shape and extend over the pivot bearing tube 46 so that the whole cradle 49 hangs freely from the pivot bearing tube and is free to swing under gravity about the axis 48 of the tube. A cable 55 extends from the hoist 14 to the sheave 50. It passes around sheaves 50 and 51 and then downwardly to a connection to the top drill rod whence it supports the drill string.
FIG. 1 shows the apparatus in a condition ready for drilling. In this condition the main part of the mast is vertical and the sheave 51 is positioned directly above the hole being drilled so that the drill string is supported by cable 55 in accurate alignment with the hole.
For hoisting operations the whole of the machine assembly 11 is drawn back along base 12 and away from the hole to the position shown in FIG. 2. The drilling head 16 is thus drawn back from its position over the hole and the drill rods can be hoisted directly past it. However the sheave 51 should be accurately positioned directly over the hole not only during drilling operations but also during hoisting. It is therefore most desirable that the position of the sheave 51 be in precisely the same position when the drilling machine is drawn back for hoisting operations as when it is in its forward position for drilling. The geometry of the illustrated arrangement is carefully arranged to produce this result.
It will be seen from FIG. 1 that when the apparatus is in condition for drilling with the machine assembly 11 in its forward position, the pivot axis 24 at the lower end of the mast is not vertically below the pivot axis 48 at the top of the mast but is positioned forwardly from such a position through a distance X. Thus although the main part of the mast is vertical the mast effectively serves as a link which is downwardly and forwardly inclined through a small angle. When the drilling machine assembly 11 is pulled back the pivot connection 18 is moved to a position 57 which is spaced horizontally from the forward position of that pivot point through a distance of 2X. The forward and rear positions of the pivot connection 18 are thus spaced one to either side of, and equally from, a vertical plane through the second position.
It will be appreciated that the forward and rear positions of the pivot connection 18 both lie on the same circular arc centered on the position of axis 48. Therefore the effect of the linking of the mast to stay arm 27 is that the pivot connection 26 at the top of the mast will be in precisely the same place for the two positions of the drilling machine assembly although it may in fact move, while the machine assembly is being moved between these forward and back positions. The drilling machine assembly could be drawn back away from the hole in a straight horizontal path. In this case the pivot position 26 would in fact move upwardly through the first half of the movement of the assembly and would then return back to its original position. Because the position of the pivot bearing tube 16 is precisely the same for the forward and back positions of the drilling machine, the sheave carriage 49 also hangs in precisely the same position although the mast has moved relative to it.
The drilling machine assembly 11 is in fact not drawn back in a straight horizontal path. As can be seen in FIGS. 4 and 5 the assembly 11 is mounted on the base 12 via front support collars 61 and rear support collars 62 which slide on front tubular rails 63 and rear tubular rails 64 fitted to the base. The rear rails 64 are inclined upwardly and rearwardly so that the whole of the drilling machine assembly 11 is canted when it is drawn back to its rear position. The arrangement is such that the pivot connection 18 adopts position 57 when the assembly 11 is drawn back to its fullest extent, i.e. the same position which it would adopt if the assembly were drawn back in a straight line. It will be appreciated that in order to maintain a straight line motion of the pivot joint 18 the machine assembly 11 would have to be mounted on a curvilinear track support. By the provision of the straight support rails the pivot connection 18 will go through transient positions away from a straight line path but when the assembly has been drawn to its rear-most position the pivot connection 18 is in the position 57 so that the pivot sheave 51 is correctly aligned above the hole.
The canting of the assembly 11 is provided in order to avoid the top of the drill string from fouling the mast during racking back. It is usual to leave the top drill rod 60 engaged with the drilling head during racking back to avoid the necessity to break the water supply and control connections made to it. The top drill rod 60 is unscrewed from the remainder of the drill string and is then drawn back with the drilling head and out of the way before the remainder of the drill string 65 is hoisted as shown in FIG. 2. If the drilling machine assembly 11 were drawn back in a straight path the top of its top rod would foul the top of the mast. However, in the illustrated arrangement the tilting of the drilling machine assembly 11, and therefore the drilling head 16, is sufficient to cant the top drill rod so that it clears the mast.
As will be seen by comparing FIGS. 1 and 2, the drilling head tilts through a rather smaller angle than does the mast as the drilling machine assembly is racked back. When the assembly 11 is in the drilling position the top drill rod 60 is generally parallel with the front face of the mast but when assembly 11 has been racked back it is inclined to the front face of the mast. This is necessary to allow the remainder of the drill string 65 to be hoisted without fouling the top of drill rod 60. The tilting movement of the drilling head 16 in fact corresponds to swinging movement about a pivot located about twice as far away as the top of the mast.
Because of the tilting movement of the machine assembly 11, it is possible to employ a simple box section mast which can be a light-weight construction. If the machine assembly 11 were not canted during racking back it would be necessary to form the mast with a recessed construction to receive the top of the drill rod and this would necessitate a mast of much more complicated and heavier construction.
The machine assembly 11 is driven backwardly and forwardly along the rails 63,64 by operation of a double acting hydraulic ram 66 pivotally connected between the assembly and the base 12. It will be seen that support collars 61, 62 are not cylindrical but their internal surfaces are conically tapered at their ends 61A, 61B, 62A, 62B and that the rails are mounted between members which define similarly tapered plugs 68A, 68B, 69A, 69B. When the machine assembly 11 is driven forwardly the tapered ends 61A, 62A engage the tapered plugs 68A, 69A whereby the machine assembly is positively located and firmly locked in position merely by maintaining hydraulic pressure of the ram 66. Similarly, the assembly is positively located and firmly locked in its rearward position by the engagement of the tapered surfaces 61B, 62B with the plugs 68B, 69B. There is therefore no need to fasten and unfasten clamping means before and after each racking operation as in conventional apparatus.
1. Field of Invention
This invention relates to drilling apparatus and particularly to core drilling apparatus used in exploratory drilling.
2. Description of Prior Art
The invention has particular but not exclusive application to small drilling rigs and is concerned with rigs of the type having a drilling machine which can be moved back and forth between a forward drilling position and a rearward hoisting position. In apparatus of this type the drilling machine assembly generally comprises a drive motor which drives a hoist drum at the rear of the assembly and a drilling head at the front of the assembly. During drilling the machine assembly is located in its forward position and the drilling head is then located directly over the hole being drilled. The drilling head grips and rotates the drill string which extends downwardly through it and the drill rod is supported by a hoisting rope passed over one or more sheaves at the top of the mast of the rig and then down to the hoist drum. When the drill string is to be retrieved from the hole, the whole drilling machine assembly is drawn or "racked" back to its rearward position and the drill string is hoisted directly by the hoist rope past the retracted drilling head.
For both the drilling and hoisting operations the drilling machine must be firmly locked in position and it is usual to provide a number of clamping bolts for this purpose. The necessity to release and reclamp these bolts when the drilling machine assembly is to be moved has proved to be most troublesome. A much more convenient arrangement is provided by the present invention.
SUMMARY OF THE INVENTION
The invention provides drilling apparatus of the type wherein a drilling machine assembly is movable on a base between a drilling position and a hoisting position by operation of power means and characterised in that the drilling machine assembly can be held in each of said positions by the interengagement of wedging surfaces on the machine assembly and on the base with the power means operating.
The machine assembly may be supported on a plurality of collars encompassing and slidable along respective rails on the base and the interengaging wedging surfaces may be provided at the ends of the collars and at the ends of the rails. For example, the rails can be cylindrical and the collars annular and there may be conically tapered end pieces at the ends of the rails to engage conically tapered internal surfaces of the collars.
In order that the invention may be more fully explained, one particular embodiment will now be described in some detail with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings,
FIG. 1 is a side elevation of a drilling apparatus shown in condition for drilling operations;
FIG. 2 is a side elevation of the apparatus in condition for hoisting operations;
FIG. 3 is an enlarged cross-section generally on the line 3--3 in FIG. 1;
FIG. 4 is an enlarged and part broken view of the bottom part of the apparatus when in the condition of FIG. 1; and
FIG. 5 is a view similar to that of FIG. 4 but with the apparatus in the condition of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The illustrated apparatus comprises a drilling machine assembly denoted generally as 11 and mounted on a fixed base 12 in a manner to be described below. The machine assembly 11 is of conventional construction comprising a drive motor 13 which drives a hoist 14 and a drilling head 16. An upright mast 17 is pivotally connected at its lower end to the machine assembly 11 by a pivot connection 18. For the most part mast 17 is of light-weight box girder construction comprising longitudinal stringers 19 and lattice bracing members 21, but its lower end is formed by a bracket 22 connected to the machine assembly 11 by a pivot pin forming the pivot connection 18 about an axis 24.
The upper part of mast 17 is pivotally connected at 26 to the upper end of a stay arm 27 which is inclined at an acute angle to the mast and is pivotally connected at its bottom end to an anchor 29 by a pivot connection 28. Anchor 29 is carried by a mount 31 which is fixed relative to the machine base 12 either by being connected directly to it or by being set firmly in the ground. Arm 27 comprises a central girder section 32, a bottom adjustment portion 33 and an upper portion 34. The lower adjustment portion 33 comprises a screw threaded stem 36 clamped to the bottom of the arm portion 32 by lock nuts 37 and screw-fitted into an internal thread socket member 38 which is connected to the anchor 29 by a ball joint forming the pivot connection 28.
The upper part 34 of arm 27 is bifurcated so as to have two end portions 41 extending one to either side of the upper part of the mast and pivotally connected at their upper ends to the mast by a composite pivot pin 42. The composite pivot pin comprises a central tube 43 to which the upper ends of the arm parts 41 are clamped by studs 44. Pivot tube 43 extends through a bearing tube 46 which is fixed between side plates 47 on the upper part of the mast. Thus the mast 17 and stay arm 27 can pivot relative to one another about the axis 48 of the pivot and bearing tubes 43,46.
A cradle 49 carrying a pair of head sheaves 50, 51 hangs from the pivot bearing tube 46 at the upper end of the mast. The cradle 49 comprises a frame 52 in which the sheaves 50, 51 are journalled and a pair of yoke members 53. The yoke members are of generally inverted U-shape and extend over the pivot bearing tube 46 so that the whole cradle 49 hangs freely from the pivot bearing tube and is free to swing under gravity about the axis 48 of the tube. A cable 55 extends from the hoist 14 to the sheave 50. It passes around sheaves 50 and 51 and then downwardly to a connection to the top drill rod whence it supports the drill string.
FIG. 1 shows the apparatus in a condition ready for drilling. In this condition the main part of the mast is vertical and the sheave 51 is positioned directly above the hole being drilled so that the drill string is supported by cable 55 in accurate alignment with the hole.
For hoisting operations the whole of the machine assembly 11 is drawn back along base 12 and away from the hole to the position shown in FIG. 2. The drilling head 16 is thus drawn back from its position over the hole and the drill rods can be hoisted directly past it. However the sheave 51 should be accurately positioned directly over the hole not only during drilling operations but also during hoisting. It is therefore most desirable that the position of the sheave 51 be in precisely the same position when the drilling machine is drawn back for hoisting operations as when it is in its forward position for drilling. The geometry of the illustrated arrangement is carefully arranged to produce this result.
It will be seen from FIG. 1 that when the apparatus is in condition for drilling with the machine assembly 11 in its forward position, the pivot axis 24 at the lower end of the mast is not vertically below the pivot axis 48 at the top of the mast but is positioned forwardly from such a position through a distance X. Thus although the main part of the mast is vertical the mast effectively serves as a link which is downwardly and forwardly inclined through a small angle. When the drilling machine assembly 11 is pulled back the pivot connection 18 is moved to a position 57 which is spaced horizontally from the forward position of that pivot point through a distance of 2X. The forward and rear positions of the pivot connection 18 are thus spaced one to either side of, and equally from, a vertical plane through the second position.
It will be appreciated that the forward and rear positions of the pivot connection 18 both lie on the same circular arc centered on the position of axis 48. Therefore the effect of the linking of the mast to stay arm 27 is that the pivot connection 26 at the top of the mast will be in precisely the same place for the two positions of the drilling machine assembly although it may in fact move, while the machine assembly is being moved between these forward and back positions. The drilling machine assembly could be drawn back away from the hole in a straight horizontal path. In this case the pivot position 26 would in fact move upwardly through the first half of the movement of the assembly and would then return back to its original position. Because the position of the pivot bearing tube 16 is precisely the same for the forward and back positions of the drilling machine, the sheave carriage 49 also hangs in precisely the same position although the mast has moved relative to it.
The drilling machine assembly 11 is in fact not drawn back in a straight horizontal path. As can be seen in FIGS. 4 and 5 the assembly 11 is mounted on the base 12 via front support collars 61 and rear support collars 62 which slide on front tubular rails 63 and rear tubular rails 64 fitted to the base. The rear rails 64 are inclined upwardly and rearwardly so that the whole of the drilling machine assembly 11 is canted when it is drawn back to its rear position. The arrangement is such that the pivot connection 18 adopts position 57 when the assembly 11 is drawn back to its fullest extent, i.e. the same position which it would adopt if the assembly were drawn back in a straight line. It will be appreciated that in order to maintain a straight line motion of the pivot joint 18 the machine assembly 11 would have to be mounted on a curvilinear track support. By the provision of the straight support rails the pivot connection 18 will go through transient positions away from a straight line path but when the assembly has been drawn to its rear-most position the pivot connection 18 is in the position 57 so that the pivot sheave 51 is correctly aligned above the hole.
The canting of the assembly 11 is provided in order to avoid the top of the drill string from fouling the mast during racking back. It is usual to leave the top drill rod 60 engaged with the drilling head during racking back to avoid the necessity to break the water supply and control connections made to it. The top drill rod 60 is unscrewed from the remainder of the drill string and is then drawn back with the drilling head and out of the way before the remainder of the drill string 65 is hoisted as shown in FIG. 2. If the drilling machine assembly 11 were drawn back in a straight path the top of its top rod would foul the top of the mast. However, in the illustrated arrangement the tilting of the drilling machine assembly 11, and therefore the drilling head 16, is sufficient to cant the top drill rod so that it clears the mast.
As will be seen by comparing FIGS. 1 and 2, the drilling head tilts through a rather smaller angle than does the mast as the drilling machine assembly is racked back. When the assembly 11 is in the drilling position the top drill rod 60 is generally parallel with the front face of the mast but when assembly 11 has been racked back it is inclined to the front face of the mast. This is necessary to allow the remainder of the drill string 65 to be hoisted without fouling the top of drill rod 60. The tilting movement of the drilling head 16 in fact corresponds to swinging movement about a pivot located about twice as far away as the top of the mast.
Because of the tilting movement of the machine assembly 11, it is possible to employ a simple box section mast which can be a light-weight construction. If the machine assembly 11 were not canted during racking back it would be necessary to form the mast with a recessed construction to receive the top of the drill rod and this would necessitate a mast of much more complicated and heavier construction.
The machine assembly 11 is driven backwardly and forwardly along the rails 63,64 by operation of a double acting hydraulic ram 66 pivotally connected between the assembly and the base 12. It will be seen that support collars 61, 62 are not cylindrical but their internal surfaces are conically tapered at their ends 61A, 61B, 62A, 62B and that the rails are mounted between members which define similarly tapered plugs 68A, 68B, 69A, 69B. When the machine assembly 11 is driven forwardly the tapered ends 61A, 62A engage the tapered plugs 68A, 69A whereby the machine assembly is positively located and firmly locked in position merely by maintaining hydraulic pressure of the ram 66. Similarly, the assembly is positively located and firmly locked in its rearward position by the engagement of the tapered surfaces 61B, 62B with the plugs 68B, 69B. There is therefore no need to fasten and unfasten clamping means before and after each racking operation as in conventional apparatus.