AU2021203426A1 - Improvements relating to pivot pins for revolute joints - Google Patents

Abstract

The present disclosure relates to a pin assembly for a revolute joint of an articulated arm or boom. In one aspect, the pin assembly comprises at least a first taper pin piece, a second taper pin piece, and a bolt for securing the first taper pin piece and the second taper pin piece together in an oppositely directed endwise arrangement, wherein the first taper pin piece and the second taper pin piece each comprises a mutually engaging end portion which will engage with each other when the taper pin pieces are joined together using the bolt in their oppositely directed endwise arrangement. 6/6 300 70 50 5480 -- 80B 60 Fig. 12

Description

6/6

300

70

50

5480

-- 80B

60

Fig. 12

IMPROVEMENTS RELATING TO PIVOT PINS FOR REVOLUTE JOINTS PRIORITY DOCUMENTS

[0001] The present application claims priority from Australian Provisional Patent Application No. 2020901821 titled "IMPROVEMENTS RELATING TO PIVOT PINS FOR BOOM PIVOTS" and filed on 3 June 2020, the content of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

[0002] The present disclosure relates to a revolute joint of the type employed in an articulated armor boom, and to a pivot pin for such a joint. An example of one use for the revolute joint is described in relation to a link for a drill positioning unit of a drill assembly, but it is not so limited in application.

BACKGROUND

[0003] A typical mobile drill rig comprises a mobile platform supporting an articulated arm boom which carries an attachment mount for a drill. The mobile platform will typically roll on either of wheels or caterpillar tracks. The boom and attachment mount will comprise a number of revolute joints to permit articulation for positioning.

[0004] Atypical revolute joint comprises a clevis, a tang, and a pin which is secured in the tang, and the ends of which engage with opposing portions of the clevis so that the clevis may pivot relative to the tang. Bushes are typically provided between each of the clevis, tang and pin.

[0005] The pivot pins are typically straight, with parallel sides, so they require a clearance hole in the tang to allow for assembly, and this clearance is a point of concentration for shock loading and wear, reducing the life of the pin and bush arrangement.

[0006] This clearance region on the non-pivoting point surface can be damaged, oversized and/or subject to ovulation, making disassembly for inspection or repair difficult and in some cases impossible without costly and time consuming welding and/or machining of the tang before the system can be re-bushed and re-assembled.

[0007] Pins also require greasing through a housing into a gap between the bushes, and full expulsion of contaminant is not possible because grease cannot flow across the outer bush.

[0008] Typical straight pins also generally require a bolt or dowel to prevent the pin from pivoting with respect to the tang, and this bolt or dowel is difficult to fit, remove, and is another common failure point.

[0009] It is against this background and the problems and difficulties associated therewith that the present disclosure has been developed.

[0010] Certain objects and advantages of the present disclosure will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.

SUMMARY

[0011] According to a first aspect, there is provided a pin assembly for a revolute joint, the pin assembly comprising at least a first taper pin piece, a second taper pin piece, and a bolt for securing the first taper pin piece and the second taper pin piece together in an oppositely directed endwise arrangement, wherein the first taper pin piece and the second taper pin piece each comprises a mutually engaging end portion which will engage with each other when the taper pin pieces are joined together using the bolt in their oppositely directed endwise arrangement.

[0012] In one form, the first taper pin piece comprises a through hole extending lengthwise therethrough, where this through hole is sized to provide a clearance around a shank of the bolt, and the second taper pin piece comprises a threaded hole extending lengthwise therethrough, where the threaded hole is adapted to threadably receive a threaded portion of the shank of the bolt.

[0013] In one form, the mutually engaging end portion of the second taper pin piece comprises a spigot, and the mutually engaging end portion of the first taper pin piece comprises a socket sized to receive the spigot.

[0014] In one form, the socket is surrounded by a collar.

[0015] In one form in an alternative, the mutually engaging end portion of the first taper pin piece comprises a spigot, and the mutually engaging end portion of the second taper pin piece comprises a socket sized to receive the spigot.

[0016] In one form, in an alternative, the mutually engaging end portions comprise cooperating male and female castellations.

[0017] According to a further aspect, there is provided a pin assembly for a revolute joint, the pin assembly comprising at least a first pin piece, a second pin piece, and a bolt for securing the first pin piece and the second pin piece together endwise, wherein the first pin piece comprises a through hole extending lengthwise therethrough, where this through hole is sized to provide a clearance around a shank of the bolt, wherein the second pin piece comprises a threaded hole extending lengthwise therethrough, where the threaded hole is adapted to threadably receive a threaded portion of the shank of the bolt, wherein one of either of the first or the second pin pieces comprises a spigot, and the other of the pin pieces comprises a socket sized to receive the spigot, and wherein both of the pin pieces diametrically taper down towards the spigot and the socket respectively.

[0018] According to a further aspect, there is provided a pin assembly for a revolute joint, the pin assembly comprising at least a first pin piece, a second pin piece, and a bolt for securing the first pin piece and the second pin piece together endwise, wherein the first pin piece comprises a through hole extending lengthwise therethrough, where this through hole is sized to provide a clearance around a shank of the bolt, wherein the second pin piece comprises a threaded hole extending lengthwise therethrough, where the threaded hole is adapted to threadably receive a threaded portion of the shank of the bolt, wherein the first pin piece comprises a spigot, and the second pin piece comprises a socket sized to receive the spigot, and wherein the first pin piece diametrically tapers down towards the spigot, and the second pin piece diametrically tapers down towards the socket.

[0019] According to a further aspect, there is provided a pin assembly for a revolute joint, the pin assembly comprising at least a first pin piece, a second pin piece, and a bolt for securing the first pin piece and the second pin piece together endwise to form a pin, wherein the first pin piece comprises a through hole extending lengthwise therethrough, where this through hole is sized to provide a clearance around a shank of the bolt, wherein the second pin piece comprises a threaded hole extending lengthwise therethrough, where the threaded hole is adapted to threadably receive a threaded portion of the shank of the bolt, wherein the second pin piece comprises a spigot, and the first pin piece comprises a socket sized to receive the spigot, and wherein the first pin piece diametrically tapers down towards the socket, and the second pin piece diametrically tapers down towards the spigot.

[0020] In one form, the pin assembly further comprises a first pair of bushes, each of which is for insertion in a tang portion, and each of which comprises a through bore comprising an internal diametric taper.

[0021] In one form, a first bush from the first pair of bushes comprises a through bore comprising an internal diametric taper to match the taper of the first pin piece.

[0022] In one form, a second bush from the first pair of bushes comprises a through bore comprising an internal diametric taper to match the taper of the second pin piece.

[0023] In one form, a tip portion of the collar surrounding the socket is a received in an opposing bush from the first pair of bushes. The opposing bush is the one provided for the opposing pin piece. The opposing pin piece is the one comprising the spigot in this case.

[0024] That is to say, the tip portion of the collar is received in the bore of the opposing bush.

[0025] In one form, the tip portion of the collar is untapered. That is to say, it is not tapered, or comprises a constant external diameter.

[0026] In one form then, a portion of the through bore in the bush comprises an internal diameter corresponding with the external diameter of the tip portion of the collar.

[0027] In one form, a first portion of the through bore in the bush comprises an internal diameter corresponding with the external diameter of the tip portion of the collar, and a second portion of the through bore comprises an internal diametric taper to match the taper of the opposing pin piece.

[0028] In one form, in an alternative, the tip portion of the collar is tapered.

[0029] In one form then, a portion of the through bore in the second bush comprises a second internal diametric taper to match the taper of the tip portion of the collar.

[0030] In one form, a first portion of the through bore in the second bush comprises a first internal diametric taper to match the taper of the opposing pin piece, and a second portion of the through bore comprises a second internal diametric taper to match the taper of the tip portion of the collar.

[0031] In one form, the pin assembly further comprises a second pair of bushes, each of which is for insertion in a clevis, and each of which comprises a through bore comprising a substantially constant internal diameter.

[0032] According to a further aspect, there is provided a revolute joint assembly comprising a clevis and a tang, wherein both the clevis and the tang comprise a matching through hole, the revolute joint assembly further comprising the above described pin assembly, wherein in use, the pin assembly is assembled in the aligned through holes of the clevis and the tang.

[0033] According to a further aspect, there is provided a boom pivot assembly comprising a first boom portion and a second boom portion, wherein the first boom portion comprises a clevis and the second boom portion comprises a tang, wherein both the clevis and the tang comprise a matching through hole, the boom pivot assembly further comprising the above described pin assembly, wherein in use, the pin assembly is assembled in the aligned through holes of the clevis and the tang.

[0034] According to a further aspect, there is provided a drill positioning unit assembly comprising a first body portion and a second body portion, wherein the first body portion comprises a clevis and the second body portion comprises a tang, wherein both the clevis and the tang comprise a matching through hole, the drill positioning unit assembly further comprising the above described pin assembly, wherein in use, the pin assembly is assembled in the aligned through holes of the clevis and the tang.

[0035] For ease of description, a drill positioning unit (DPU) employing a plurality of revolute joints is described below in its usual assembled position as shown in the accompanying drawings and terms such as front, rear, upper, lower, horizontal, longitudinal etc., may be used with reference to this usual position. However, the invention may be manufactured, transported, sold, or used in orientations other than that described and shown here.

BRIEF DESCRIPTION OF DRAWINGS

[0036] Forms of the present disclosure will be discussed with reference to the accompanying drawings wherein:

[0037] Figure 1 is an isometric view of a drill positioning unit;

[0038] Figure 2 is an isometric view of the drill positioning unit from a further viewpoint;

[0039] Figure 3 is a side view of the drill positioning unit;

[0040] Figure 4 is top view of the drill positioning unit;

[0041] Figure 5 is an end view of the drill positioning unit;

[0042] Figure 6 is a side view of the DPU;

[0043] Figure 7 is a further side view of the DPU;

[0044] Figure 8 is a top view of the DPU;

[0045] Figure 9 is a cross-sectional view through the DPU taken at A-A;

[0046] Figure 10 is a cross-sectional view through the DPU taken at B-B;

[0047] Figure 11 is an exploded view of the drill positioning unit;

[0048] Figure 1la is a cross-sectional view through pin assembly 200;

[0049] Figure 1lb is a cross-sectional view through pin assembly 100;

[0050] Figure 1Ic is a cross-sectional view through pin assembly 40; and

[0051] Figure 12 is a cross-sectional view through a further pin assembly.

[0052] In the following description, like reference characters designate like or corresponding parts throughout the figures.

DESCRIPTION OF EMBODIMENTS

[0053] Referring now to Figures 1 and 2, where there is shown a drill positioning unit (DPU) 1 for mounting a drill assembly (not illustrated) to a drill boom (i.e. an articulated arm - not illustrated) of a drill rig (not illustrated) of the type which might comprise a mobile platform (not illustrated) which rolls on caterpillar tracks or wheels (not illustrated).

[0054] The drill assembly typically comprises a mast supporting a drill. The drill could be either of a hammer drill or a rotary drill, but is not so limited.

[0055] At this point it should be made clear that the present invention is not limited to use in a DPU, but may be employed wherever a revolute joint of this type is required, such as (but not limited to) in the articulated arm of the drill boom, or even a boom of an excavator.

[0056] Referring now to Figure 11, the DPU 1 comprises a first body portion 2 and a second body portion 4. The first body portion 2 is connected to the drill boom via first revolute joint A. This first revolute joint A comprises a first pin assembly 40 passed through a tang 6 provided on the first body portion 2 of the DPU 1, and a clevis (not illustrated) provided on the drill boom.

[0057] The first body portion 2 and the second body portion 4 are connected by a second revolute joint B oriented at 90° to the first revolute joint A, so that the DPU 1 can act like a universal joint between the drill boom and the drill assembly. This second revolute joint B comprises a second pin assembly 100 passed through a clevis 8 provided on the first body portion 2 of the DPU 1, and a tang 10 provided on the second body portion 4 of the DPU 1.

[0058] The drill assembly will depend from a slewing drive mounted to a flange 12 provided on the second body portion 4 of the DPU 1.

[0059] The first body portion 2 further comprises an attachment clevis 14 which will form part of third revolute joint C via which a drive cylinder extending from the boom is attached to the first body portion 2. The first and third revolute joints A and C each comprise an axis of rotation which is extending substantially parallel to each other. No pin is illustrated, but this third revolute joint C could employ a further pin assembly, similar to the first pin assembly 40.

[0060] Similarly, the second body portion 4 further comprises an attachment clevis 16 via which a drive cylinder extending from the boom is attached to the second body portion 4 via an attachment link 18 and a fourth revolute joint D. The second and fourth revolute joints B and D each comprise an axis of rotation which is extending substantially parallel to each other.

[0061] This fourth revolute joint D comprises a third pin assembly passed through the clevis 16 provided on the second body portion 4 of the DPU 1, and a tang 20 provided on the link 18. The link 18 comprises a clevis which will form part of a further revolute joint with the drive cylinder. Again, no pin is illustrated, but this revolute joint could employ a further pin assembly, similar to the first pin assembly 40.

[0062] The first pin assembly 40 comprises at least a first pin piece 50, a second pin piece 60, and a bolt for securing the first pin piece 50 and the second pin piece 60 together endwise to form a pin about which the revolute joint will pivot. The first pin piece 50 comprises a through hole 52 extending lengthwise therethrough, where this through hole 52 is sized to provide a clearance around a shank 72 of the bolt 70. The second pin piece 60 comprises a threaded hole 62 extending lengthwise therethrough, where the threaded hole 62 is adapted to threadably receive a threaded portion of the shank 72 of the bolt 70.

[0063] The second pin piece 60 further comprises a spigot 64, and the first pin piece 50 comprises a socket 54 sized and shaped to receive the spigot 64 which will engage with each other when the pin pieces are joined together using the bolt, in their oppositely directed endwise arrangement. The socket 54 is surrounded by a collar 55.

[0064] The first pin piece 50 diametrically tapers down towards the socket 54. More particularly, the first pin piece comprises a parallel portion 56 of substantially constant diameter, and a tapered portion 58 which diametrically tapers down towards the socket 54.

[0065] Similarly, the second pin piece 60 diametrically tapers down towards the spigot 64. More particularly, the second pin piece 60 comprises a parallel portion 66 of substantially constant diameter, and a tapered portion 68 which diametrically tapers down towards the spigot 64.

[0066] The first pin assembly 40 further comprises a first pair of bushes 80A and 80B, each of which is for insertion in a tang portion 6, and each of which comprises a through bore comprising an internal diametric taper.

[0067] A first bush 80A from the first pair of bushes comprises a through bore 82 comprising an internal diametric taper to match the taper 58 of the first pin piece 50.

[0068] A second bush 80B from the first pair of bushes comprises a through bore 82 comprising an internal diametric taper to match the taper 68 of the second pin piece 60.

[0069] In use, the bolt 70 is placed in tension and it pulls the pin pieces 50 and 60 together and drives each pin piece 50 or 60 against its respective opposing tapered bush 80A or 80B.

[0070] The pin assembly 40 further comprises a second pair of bushes 90A and 90B, each of which is for insertion in one of the opposing portions of a clevis (associated with the boom in this case, and so not illustrated), and each of which comprises a through bore 92 comprising a substantially constant internal diameter.

[0071] A first bush 90A from the second pair of bushes comprises a through bore 92 comprising a substantially constant internal diameter to match parallel portion 56 of the first pin piece 50.

[0072] A second bush 90B from the second pair of bushes comprises a through bore 92 comprising a substantially constant internal diameter to match parallel portion 66 of the second pin piece 60.

[0073] Each of the bushes 80A,B and 90A,B comprises a flange providing a thrust wear surface, making thrust wear repairable by way of bush replacement, and eliminating the need for machining to correct thrust wear.

[0074] A flat O-ring gasket seal 94 is provided between each pair of oppositely directed first and second bushes 90A and 90B.

[0075] Each of the pin pieces 50 and 60 comprises a jacking (pulling) thread in an outer end of its through hole, via which these pin pieces 50 and 60 can be pulled apart. In the first pin piece 50, this jacking thread is sized to provide a clearance around the bolt 70. Once the taper is dislodged, the system comes apart simply and easily.

[0076] The third pin assembly 200 differs from the first pin assembly in its sizing, but is otherwise near identical in arrangement. Accordingly, those parts of the third pin assembly 200 which are identical (or near- identical) to corresponding parts of the first pin assembly 40 will be denoted by the same reference numerals and will not be described again in detail.

[0077] It can be seen that the third revolute joint D comprises a pair of end caps 96 with sealing gaskets 97 and retaining bolts 98 for closing and sealing the ends thereof, and protecting the pin assembly 200 from ingress of dirt and moisture.

[0078] While not illustrated (owing to omission of the boom clevis), it should be understood that the first revolute joint A would include similar end caps 96, sealing gaskets 97 and retaining bolts 98. Grease is applied by removal of the caps 96, ensuring correct full expulsion of contaminant from bushing areas and thorough lubrication of the entire bushing surface.

[0079] The second pin assembly 100 differs from the first pin and third pin assemblies in sizing, but also in a further salient respect.

[0080] The second pin assembly 100 comprises at least a first pin piece 150, a second pin piece 160, and a bolt 70 for securing the first pin piece 150 and the second pin piece 160 together endwise to form a pin. The first pin piece 150 comprises a through hole 152 extending lengthwise therethrough, where this through hole 152 is sized to provide a clearance around a shank 72 of the bolt 70. The second pin piece 160 comprises a threaded hole 162 extending lengthwise therethrough, where the threaded hole 162 is adapted to threadably receive a threaded portion of the shank 72 of the bolt 70.

[0081] The first pin piece 150 comprises a spigot 154, and the second pin piece 160 comprises a socket 164 sized and shaped to receive the spigot 154, so that these engage with each other when the taper pin pieces 150 and 160 are joined together using the bolt 70, in their oppositely directed endwise arrangement. This arrangement of socket and spigot is the reverse of that in pin assemblies 40 and 200.

[0082] Those parts of the third pin assembly 100 which are identical (ornear-identical) to corresponding parts of the first pin assembly 40 and second pin assembly 200 will be denoted by the same reference numerals and will not be described again in detail.

[0083] Referring now to Figure 12, where there is illustrated yet a further pin assembly 300. Those parts of the pin assembly 300 which are identical (or near- identical) to corresponding parts of the first pin assembly 40 will be denoted by the same reference numerals and will not be described again in detail.

[0084] Pin assembly 300 differs from above described examples primarily, though not exclusively, in that a tip portion of the collar 55 surrounding the socket 54 is received in an opposing bush 80B from the first pair of bushes 80A, 80B.

[0085] The tip portion of the collar 55 is untapered. That is to say, it comprises a constant external diameter.

[0086] A portion of the through bore in the opposing bush 80B comprises an internal diameter corresponding with the external diameter of the tip portion of the collar 55. In other words, a first portion of the through bore in the second bush 80B comprises the internal diameter corresponding with the external diameter of the tip portion of the collar 55, and a second portion of the through bore comprises an internal diametric taper to match the external taper of the opposing pin piece 60.

[0087] The bushes 80A and 80B extend towards each other and come close to meeting, but do not come into contact.

[0088] An advantage of this arrangement is that the pin piece 50 comprising the collar 55 is supported throughout a region extending from its tapered portion to its collar 55 tip in the opposing (i.e. second) bush 80B. The opposing pin piece 60 is supported throughout a region extending from its tapered portion to its spigot 64, which is supported in the socket 54 of the first pin piece 50. The greater the distance between these upper and lower support positions the greater bearing or support area and the greater the degree of support and the stronger the pin assembly 300.

[0089] Advantageously, the pin assembly according to the present disclosure eliminates the clearance fit of a typical parallel pin and replaces this with a taper system to remove all clearance, wear, and shock load, and to lock the pin assembly in place without need for a dowel or bolt. The aperture provided for the dowel or bolt may instead be used to accommodate a pin position sensor.

[0090] The longitudinal engagement of the two pin pieces greatly increases the strength, rigidity and holding ability of the pin assembly when compared with a typical, single straight pin.

[0091] Incorporating thrust and sealing wear surfaces into the female taper and straight bushes make all remaining wear parts simple to replace without need for welding and machining.

[0092] Advantages over typical pins will be seen firstly in system service life being increased, and improved sealing provided by using replaceable seal surfaces.

[0093] Further advantage is greatly reduced repair cost and time due to all wear parts and surfaces being replaceable in a field or workshop situation.

[0094] Throughout the specification and the claims that follow, unless the context requires otherwise, the words "comprise" and "include" and variations such as "comprising" and "including" will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

[0095] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.

[0096] It will be appreciated by those skilled in the art that the invention is not restricted in its use to the particular application described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that the invention is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention as set forth and defined by the following claims.

Claims (16)

1. A pin assembly for a revolute joint, the pin assembly comprising at least a first taper pin piece, a second taper pin piece, and a bolt for securing the first taper pin piece and the second taper pin piece together in an oppositely directed endwise arrangement to form a pin, wherein the first taper pin piece and the second taper pin piece each comprises a mutually engaging end portion which will engage with each other when the taper pin pieces are joined together using the bolt, in their oppositely directed endwise arrangement.

2. The pin assembly of claim 1, wherein the first taper pin piece comprises a through hole extending lengthwise therethrough, where this through hole is sized to provide a clearance around a shank of the bolt, and the second taper pin piece comprises a threaded hole extending lengthwise therethrough, where the threaded hole is adapted to threadably receive a threaded portion of the shank of the bolt.

3. The pin assembly as in either of the preceding claims, wherein the mutually engaging end portion of the second taper pin piece comprises a spigot, and the mutually engaging end portion of the first taper pin piece comprises a socket sized to receive the spigot.

4. The pin assembly as in either of claims 1 or 2, wherein the mutually engaging end portion of the first taper pin piece comprises a spigot, and the mutually engaging end portion of the second taper pin piece comprises a socket sized to receive the spigot.

5. A pin assembly for a revolute joint, the pin assembly comprising at least a first pin piece, a second pin piece, and a bolt for securing the first pin piece and the second pin piece together endwise to form a pin, wherein the first pin piece comprises a through hole extending lengthwise therethrough, where this through hole is sized to provide a clearance around a shank of the bolt, wherein the second pin piece comprises a threaded hole extending lengthwise therethrough, where the threaded hole is adapted to threadably receive a threaded portion of the shank of the bolt, wherein one of either of the first or the second pin pieces comprises a spigot, and the other of the pin pieces comprises a socket sized to receive the spigot, and wherein both of the pin pieces diametrically taper down towards the spigot and the socket.

6. A pin assembly for a revolute joint, the pin assembly comprising at least a first pin piece, a second pin piece, and a bolt for securing the first pin piece and the second pin piece together endwise to form a pin, wherein the first pin piece comprises a through hole extending lengthwise therethrough, where this through hole is sized to provide a clearance around a shank of the bolt, wherein the second pin piece comprises a threaded hole extending lengthwise therethrough, where the threaded hole is adapted to threadably receive a threaded portion of the shank of the bolt, wherein the first pin piece comprises a spigot, and the second pin piece comprises a socket sized to receive the spigot, and wherein the first pin piece diametrically tapers down towards the spigot, and the second pin piece diametrically tapers down towards the socket.

7. A pin assembly for a revolute joint, the pin assembly comprising at least a first pin piece, a second pin piece, and a bolt for securing the first pin piece and the second pin piece together endwise to form a pin, wherein the first pin piece comprises a through hole extending lengthwise therethrough, where this through hole is sized to provide a clearance around a shank of the bolt, wherein the second pin piece comprises a threaded hole extending lengthwise therethrough, where the threaded hole is adapted to threadably receive a threaded portion of the shank of the bolt, wherein the second pin piece comprises a spigot, and the first pin piece comprises a socket sized to receive the spigot, and wherein the first pin piece diametrically tapers down towards the socket, and the second pin piece diametrically tapers down towards the spigot.

8. The pin assembly as in any one of the preceding claims, further comprising a first pair of bushes, each of which is for insertion in a tang portion of a revolute joint, and each of which comprises a through bore comprising an internal diametric taper.

9. The pin assembly of claim 8, wherein a first bush from the first pair of bushes comprises a through bore comprising an internal diametric taper to match the taper of the first pin piece.

10. The pin assembly of claim 8, wherein a second bush from the first pair of bushes comprises a through bore comprising an internal diametric taper to match the taper of the second pin piece.

11. The pin assembly as in any one of claims 8 through 10, wherein a tip portion of the collar surrounding the socket is received in the through bore of an opposing bush from the first pair of bushes.

12. The pin assembly as in any one of claims 8 through 11, wherein the first pair of bushes extend towards each other and come close to meeting, but do not come into contact.

13. The pin assembly as in any one of claims 8 through 10, wherein the pin assembly further comprises a second pair of bushes, each of which is for insertion in a clevis portion of a revolute joint, and each of which comprises a through bore comprising a substantially constant internal diameter.

14. A revolute joint assembly comprising a clevis and a tang, wherein both the clevis and the tang comprise a matching through hole, the revolute joint assembly further comprising the above described pin assembly, wherein in use, the pin assembly is assembled in the aligned through holes of the clevis and the tang.

15. A boom pivot assembly comprising a first boom portion and a second boom portion, wherein the first boom portion comprises a clevis and the second boom portion comprises a tang, wherein both the clevis and the tang comprise a matching through hole, the boom pivot assembly further comprising the pin assembly according to any one of the preceding claims, wherein in use, the pin assembly is assembled in the aligned through holes of the clevis and the tang.

16. A drill positioning unit assembly comprising a first body portion and a second body portion, wherein the first body portion comprises a clevis and the second body portion comprises a tang, wherein both the clevis and the tang comprise a matching through hole, the drill positioning unit assembly further comprising the pin assembly according to any one of claims 1 through 9, wherein in use, the pin assembly is assembled in the aligned through holes of the clevis and the tang.