US3919816A

US3919816A - Mast supporting adjustability device

Info

Publication number: US3919816A
Application number: US466076A
Authority: US
Inventors: Eberhard V Ranft
Original assignee: Raymond International Inc
Current assignee: Raymond International Inc
Priority date: 1974-05-01
Filing date: 1974-05-01
Publication date: 1975-11-18
Anticipated expiration: 1992-11-18
Also published as: CA1023126A

Abstract

A drill rig having a universally mounted mast which is rigidly supported but moveable both transversely and rotationally in fore and aft and lateral directions. Novel mast support arrangements are disclosed including a free floating upper brace to accomodate relative vertical displacements of mast connection points which occur during rotational or tilting movements of the mast, and further including upper and lower crossbeams with connector elements separately moveable therealong and pivotally connected to the mast.

Description

States Patent I MAST SUPPORTING ADJUSTABILITY DEVICE [75] Inventor: Eberhard V. Ranft, Houston, Tex.

[73] Assignee: Raymond International, Inc.,

Houston, Tex.

[22] Filed: May 1, 1974 [21] Appl. N0.: 466,076

[52] US. Cl. 52/116; 173/28; 173/43 [51] Int. Cl. E0411 12/34; 1521C 9/00 [58] Field of Search 52/111, 116, 115; 173/43, 173/28; 212/8 R, 9; 254/1391; 214/671, 75 H [56] References Cited UNITED STATES PATENTS 808,132 12/1905 Williams 173/28 2,348,024 5/1944 Parrish 173/28 X 2,598,454 5/1952 Smith 173/43 2,689,549 9/1954 Hayman 52/115 X 2,827,772 3/1958 Taylor et a1. 173/28 X 2,904,310 9/1959 Leonard 173/43 X 2,980,269 4/1961 Zimmerman 214/671 X 3,161,262 12/1964 Back 254/1391 X 3,172,483 3/1965 Spitzer 173/28 X 3,225,842 12/1965 Roeschen 173/43 3,340,938 9/1967 Wilson 173/28 Primary Examiner-Henry C. Sutherland Assistant E\'aminerLeslie A. Braun Attorney, Agent, or Firm-Fitzpatrick, Cella, Harper & Scinto ABSTRACT A drill rig having a universally mounted mast which is rigidly supported but moveable both transversely and rotationally in fore and aft and lateral directions. Novel mast support" arrangements are disclosed including a free floating upper brace to accomodate relative vertical displacements of mast connection points which occur during rotational or tilting movements of the mast, and further including upper and lower crossbeams with connector elements separately moveable therealong and pivotally connected to the mast.

15 Claims, 12 Drawing Figures Sheet 1 of8 US. Patent Nov. 18, 1975 US. Patent Nov. 18, 1975 Sheet 2 of8 3,919,816

US. Patent Nov. 18, 1975 Sheet3of8 3,919,16

Ticll.

US. Patent Nov. 18,1975 Sheet60f8 3,919,816

US. Patfiznt Nov. 18, 1975 Sheet 8 of8 3,919,816

MAST SUPPORTING ADJUSTABILITY DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to moveable mast support mechanisms and more particularlyit concerns novel structures for adjustably supporting a mastin different transverse and lateral positions as well as-in different degrees of rotation or tilt with respect to the base on which it is mounted. The present invention is particularly suited to portable drill rigs and to other typesof derrick which are required toposition an elongated mast-like structure, such as a drill guide, accurately over predetermined locations, in the earth and to maintainthe structure firmly at a given degree of tilt while a dr illing or other operation is carried out.

The present invention makes it possible for a drilling rig to support its drilling mast rigidly at each o f-a range of transverse and fore and aft locations and to adjust the position of the mast with respect to the drilling rig structure with high degree of accuracy. In addition the present invention also permits the drilling mast to be tilted or rotated in both the fore and aft and lateral planes; and it also enables the mast to be retracted from its operative upright position to a horizontal position atop the rig so that the rig can ,be transported along highways and other routes requiring a limited overall vehicle height. I

2. Description of Known Prior Art U.$. Pat. Nos. 3,312,221 and 3,385,014 show a pile drivingrig having a mast which is adjustably supported by means of bracing struts... The bracing struts are also arranged to allow the mast to be moved to a horizontal position atop the rig fortransporting same. The bracing strut arrangements of this known prior art, however, do

not allow so universal a movementof the mast as is obtained with the present invention nor do they support the mast as rigidlywith sofew moving parts as. is obtained with the present invention SUMMARY OF TI-IE INVENTIQN In one aspect, the present invention provides a mechanism for adjustably supporting a mast for fore and aft translational and tilting or rotational movement with respect to a base such as a drill rig chassis. According to this aspect of the invention the lowerregion of the mast is pivotally supported in front of the base by a first mounting means near one edge of the base. A rear brace is connected at one end to extend up from a second location on the base behind the first location. An upper brace is freely pivotally connected between an upper point on the mast and the other end of the rear brace; and an actuating mechanism is provided to cause the upper brace to move the upper region of the mast back and forth. The upper brace is thus not required to supportany of the mast weight and it merely needs to move the upper end of the mast fore and aft. Because the upper brace is freely pivoted with respect to the rear brace it can readily' accomodate I any changes in the vertical distance between the upper and lower mast connection points which occur when the mast is tilted. I a v I In the preferred embodiment the first mounting means also comprises a spotter brace pivotally connected between the front edge of the base and the lower point on the mast. Means are provided to control,

movements of the spotter bracein conjunction with those of. the upper brace to produce for and aft translational and rotational mast movements. Also in the preferred embodiment, the rear braceis pivotally connected to the base behind its front edge and actuating means are arranged to produce rotation of the rear brace so that the upper brace fore and aft movements can be controlled and so that the mast can be retracted to a horizontal position on top of the base for transportation. This last mentioned means may take the form of hydraulic batter piston and cylinder assemblies which extend from the base to locations at or near the upper end of the rear brace. Where the base is a vehicle v Chassis it may be provided with wheels or tracks for mobily t t Q I a According to a further aspect of the present invention there are provided arrangements for obtaining lateral transverse and rotational positioning of a mast. These arrangements include upper and lower cross beams with a mast connector element mounted for movement along each beam. The connector elements are pivotally connected to upper and lower locations, respectively, on the mast and means are provided to accomodate the different distances between the connector element-to-mast. connecting points, in the vertical direction as the mast is rotated. In the preferred embodiment, the distance between the connector element to mast connecting points is maintained fixed alongthe length of the mast and the different distances between these connecting points, which occur in the vertical direction when the mast is rotated, is accomodated by the provision of upper crossbeam mounting means which supports the beam rigidly in the fore and aft and lateral directions but allows free movement of the beam in the vertical direction.

There has thus been outlined rather broadly the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may'be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. Those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures and other methods for carrying out the several purposes of the invention. It is important, therefore, that the claims be regarded as including such equivalent structures and methods as do not depart from the spirit and scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS A specific embodiment of the invention has been chosen for purposes of illustration and description, and is shown in the accompanying drawings forming a part of the specification, wherein:

FIG. 1 is a side elevational outline view .of a drill rig in which the present invention is embodied, and illustrating fore and aft mast positioning configurations of the rig;

FIG. 2; is a front elevational outline view of the drill rig of FIG. 1, and illustrating lateral mast positioning configurations of the rig;

FIG. 3 is an enlarged sideelevational view of the drill rig of FIG. 1 in its mast retracting configuration;

FIG. 4 is a top plan view of the drill rig of FIG. 3;

FIG. Sis a further enlarged side elevational view, partially cut away, of the drill rig of FIG. I showing in detail various bracing assemblies for mast positioning;

FIG. 6 is a front elevational view, partially cut away, of the drill rig, of FIG.

FIG. 7 is a view taken along line 7-7 of FIG. 5;

FIG. 8 is a top plan view of the drill rig of FIG. 5;

FIG. 9 is an enlarged view, partially cutaway of a cross-beam and mast mounting assembly taken along line 99 of FIG. 6;

FIG. 10 is a view taken along line l0l0 of FIG. 9;

FIG. 11 is an enlarged section view taken along line 11-11 of FIG. 10; and

FIG. 12 is a fragmentary perspective view, partially exploded showing selected portions of the cross-beam mounting assembly of FIGS. 9-11;

DESCRIPTION OF THE PREFERRED EMBODIMENT The drill rig shown in FIGS. 1-4 comprises a main chassis assembly mounted on crawler tracks 22 for movement over a ground surface 24 with a maximum of traction and a minimum of unit ground pressure.

An elongated mast 26 of open framework construction is supported for controlled movements out in front of the main chassis assembly 20 by a novel system of braces. In general, this system of braces comprises a spotter brace assembly 28, a lower crossbeam assembly 30, a rear brace assembly 32, an upper brace assembly 34 and an upper crossbeam assembly 36. The spotter brace assembly 28 extends forwardly from a spotter pivot 38 on the front edge of the main chassis assembly 20 to a lower crossbeam pivot 40 on the lower crossbeam assembly 30. The lower crossbeam assembly 30, in turn is connected to a lower region of the mast 26. A brace pivot assembly 42 interconnects one end each of the rear and

upper brace assemblies

32 and 34, while the opposite end of the rear brace assembly is connected to a rear barce pivot 44 located on the main chassis assembly 20 rearwardly of the spotter pivot 38, and the opposite end of the upper brace assembly 34 is connected to an upper crossbeam pivot 46 on the upper crossbeam assembly 36. The upper crossbeam assembly in turn is connected to an upper region of the mast 26. I

An hydraulic spotter piston and cylinder assembly 48 is pivotally connected between a spotter brace assembly pivot 49 near the lower crossbeam pivot 40 and a spotter cylinder anchor point 50 located on the main chassis assembly 20 rearwardly of the spotter pivot 38. Also, an hydraulic batter piston and cylinder assembly 52 is pivotally connected between the brace pivot assembly 42 and a batter cylinder anchor point 54 located on the main chassis assembly 20 forwardly of the rear brace pivot 44.

It will be appreciated that by selective control of the extension and retraction of the spotter and batter piston and

cylinder assemblies

48 and 52, the spotter, rear and

upper brace assemblies

28, 32 and 34 can be articulated to move the mast 26 in a transverse rearward direction from its solid line position. indicated at A, to the phantom line position, indicated at B, or in both rotational and transverse directions to the phantom line positions indicated at C and D. Any intermediate rotational and transational position can also be achieved by proper control of the relative actuation of the spotter and batter piston and cylinder assemblies.

Turning now to FIG. 2, it will be seen that the mast 26 is also moveablc in a lateral direction, hoth transversely, as indicated by the phantom lines E and F, and rotationally. as indicated by the phantom line G and the solid line position H. These movements are achieved by causing either or both of the lower and

upper crossbeam assemblies

30 and 36 to move the mast laterally with respect to the lower and upper crossbeam pivots 40 and 46 respectively. The particular construction of the

crossbeam assemblies

30 and 36 and the manner in which they produce this lateral mast movement will be described more fully hereinafter.

It should be noted that the distance along the length of the mast 26 between the lower and

upper crossbeam assemblies

30 and 36 is fixed. Further, since the crossbeam assemblies remain horizontal, the vertical distance between them changes as the mast 26 is rotated or tilted between either of its vertical positions E or F and either of its rotated positions G or H. The mannner in which this vertical displacement is accomodated with the novel bracing system of the present invention can be seen in FIG. 1. It will be noted from FIG. 1 th af the upper brace assembly 34 is free to pivot via the brace pivot assembly 42 as the batter piston and cylinder assembly 52 causes the rear brace 32 to pivot about the rear brace pivot 44. The upper brace assembly 34 thus floats with respect to the remainder of the system and provides lateral stability to the upper end of the mast 26. Because of the floating capability, the upper brace assembly 34 merely pivots downwardly slightly to accomodate the varying vertical distances between the lower and

upper crossbeam assemblies

30 and 36 when they are actuated to rotate the mast 26 laterally between its vertical and tilted positions as shown in FIG. 2.

Turning now to FIGS. 3 and 4, it will be seen that the bracing system can be actuated to bring the mast 26 to a full horizontal position on top of the main chassis assembly 20. With the mast in this position the rig is quite compact and stabilized for travel either on its own crawler tracks 22 or on another vehicle.

In the enlarged views of FIGS. 3 and 4 it can be seen that the main chassis assembly 20 is provided with an operators cab 56 positioned near its front edge and offset laterally to permit retraction of the mast 26 to its horizontal position. Toward the rear of the main chassis assembly there is provided an engine compartment 58 wherein a crawler track driving engine is mounted. A main fuel tank 60 is located aft of the engine compartment 58. The region forwardly of the engine compartment is taken up with various power supply equipment for the drilling or other operations which the rig is to provide. Also hydraulic power and control apparatus for actuation of the spotter and batter piston and cylinder assemblies and other hydarulic apparatus on the rig.

It will be noted from FIG. 3 that when the mast 26 is in its horizontal fully retracted position, the brace system is articulated such that it is essentially fully collapsed, with the batter piston and cylinder assembly 52 fully extended. While this does provide a very compact arrangement for transportation, it also reduces the mechanical advantage or leverage available to the batter piston and cylinder assembly 52 in the initial stages of mast erection. In order to reduce the initial loading on the batter piston and cylinder assembly during the early stages of mast erection, there is provided an hydraulic booster piston and cylinder assembly 62. This assembly extends essentially vertically from a booster anchor 64 on the main chassis assembly 20 to a pusher pad 66 which rests against the side of the mast 26 in its horizontal position. The manner in which this booster piston and cylinder assembly operates can best be seen in FIG. 5. During the initial stages of mast erection, the booster piston and cylinder assembly are actuated and extended to urge the mast 26 upwardly so that it rotates about the lower crossbeam pivot 40. When the mast reaches the position indicated by the phantom outline J in FIG. 5, the brace system is articulated sufficiently to increase the mechanical advantage presented to the batter piston and cylinder assembly 52 so that by actuating this assembly in a retraction direction the brace system may continue to be articulated to bring the mast to a full upright position.

There are several additional advantages which result from the bracing and actuation system described above; and these advantages can best be appreciated from a consideration of FIG. 5 of the drawings. Firstly, the spotter brace assembly 28, along withthe spotter pivot 38, and the lower crossbeam pivot 40, cooperate to form a lower mounting arrangement by which the lower region of the mast 26 is pivotally mounted to the front edge of the main chassis assembly 20. This lower mounting arrangement is capable of supporting all of the mast weight, including the weight of all equipment carried by the mast. The spotter brace assembly 28 extends sharply upwardly from the main chassis assembly 20 to the lower crossbeam pivot 40 so that a minimal portion of the mast weight is borne by the spotter piston and cylinder assembly 48. Further, with this arrangement, the spotter piston and cylinder assembly actuation is primarily directed to fore and aft movement of the lower region of the mast.

Because the mast weight is borne by the lower mounting arrangement, the action of rear and

upper brace assemblies

32 and 34 and the batter piston and cylinder assembly 52 is used only to control fore and aft movements of the upper regions of the mast 26. Thus, once the mast is erected to a generally upright attitude and is supported by the lower mounting assembly, positional adjustments of the upper portion of the mast can be obtained by means causing fore and aft movement of the upper crossbrace assembly 34. Where this means incorporates the rear and

upper brace assemblies

32 and 34 and the batter piston and cylinder assembly 52, the stresses imposed on these elements is only minimal. Moreover, the placement of the batter piston and cylinder assembly is such that when the mast is upright and is being positionally adjusted or spotted, the batter piston and cylinder assembly is in its more retracted condition. Also the geometry of the bracing system in this condition is such that relatively large piston and cylinder movements are needed to produce rather small amounts of mast movement. This allows for significantly fine control and accurate positioning or spotting of the mast.

When the mast is retracted to its horizontal position as shown in phantom outline in FIG. 5 the batter piston and cylinder assembly 52 is fully extended. This is due to the positioning of the batter cylinder anchor points 54 forwardly of the rear brace pivot 44. As a result, the batter piston and cylinder assembly is subjected only to tensile forces during mast retraction and erection movements. This permits a lighter weight construction than would be needed in the case where high compressive forces are encountered.

As shown in FIG. 5 a drill guide 68 and associated drilling equipment 70 are mounted on the mast 26 for drilling operations where the mast is erected. This I equipment may remain on the mast where it is retracted so that minimal dissassembly is needed for transporting the drill rig.

As can be seen in FIGS. Sand 6 the mast 26 is of scribed in detail hereinafter, may be actuated to move the mast 26 laterally as indicated by the arrows L and M. When both crossbeam assemblies produce the same amount of movement in the same direction the mast undergoes lateral translational movement; but when the crossbeam assemblies are actuated to produce different amounts of movement or movements is different directions the mast is then rotated or tilted accordingly.

It will also be seen from FIG. 6 that the spotter brace assembly 28 comprises a pair of spotter braces 28a and 28b each connected to the main chassis assembly 20 and to the lower crossbeam assembly 30 by means of individual ones of the spotter pivots 38 and the lower crossbeam pivots 40.

As shown in FIG. 7 the rear brace assembly 32 is built up of tubular steel in the form of a flat framework. The upper and lower ends of the rear brace assembly are each provided'with spaced apart knuckles 72 which form portions of the brace pivot assembly 42 and the rear brace pivot 44. The batter piston and cylinder assembly 52 also comprises a pair of batter piston and cylinders 52a and 52b each connected to spaced apart locations on the brace pivot assembly 42 and each extending down to associated batter cylinder anchor points 54.

As shown in FIG. 8, the upper brace assembly 34 is of similar construction to that of the rear brace assembly 42; and it also is provided with spaced apart knuckles 63 which form portions of the brace pivot assembly 42 and the upper crossbeam pivot 46. The framelike construction of the mast 26 and the rear and

upper brace assemblies

32 and 34 and their spaced apart pivotal interconnections results in an overall box-like configuration made up of the mast 26 the upper brace assembly 34 the rear brace assembly 32, and the main chassis assembly 20. This provides a high degree of rigidity for a relatively light weight structure. The upper and

lower crossbeam assemblies

30 and 36 are of the same construction; and accordingly only the upper crossbeam assembly 36 will be described herein. The construction of this assembly is best shown in FIGS. 6 and 9-12.

As shown in FIG. 9 the knuckles 74 of the upper brace assembly 34 are pinned to connecting lugs 76 to form the upper crossbeam pivot 46. The lugs ".76 in turn are welded to an elongated rail-like leader 78 which extends horizontally of the rig. The leader 78, as shown in FIG. 12 has upper and lower rails 80 and a central lengthwise channel 82. Further, as shown in FIGS. 9 and 11, a double rod end cylinder and piston assembly 84 is bolted to the leader 78 half way along its length and inside the channel 82. This lateral piston and cylinder assembly 84 is mounted to extend along the channel 82 with its rod ends in mutually opposite directions and fastened by pin connection 86 to puller plates 88.

The lateral piston and cylinder assembly extends out beyond the ends of the leader 78 where it is connected to the puller plates 88. These puller plates are interconnected by upper and lower flanged braces 90 which extend along parallel to and just above and below the leader 78. A leader carriage 92 is mounted between the flanged braces 90 midway along their length. This leader carriage comprises a front plate 94, and upper and lower rear plates 96 welded together in spaced apart relationship by means of gussets 115. This welded carriage assembly, consisting of

plates

94, 96 houses a group of upper and lower rollers 98 which ride on the rails 80 of the leader 78 and which have axles 100 extending through the front plate 94 and the rear plates 96. Locking nuts 102 are threaded to the axles 100 outside the plates. Cover plates 104 are fastened in place between the plates to protect the rollers 98 from infiltration of foreign matter. Further, as shown in FIG. 11, bronze wear pads 106 are provided between the plates and the sides of the rails 80 to provide smooth low friction carriage movement.

It will be seen from the foregoing that the leader 78 is secured by the lugs 76 to the upper crossbeam pivot 46 and that the carriage 92 is moveable back and forth with the rollers 98 riding on the rails 80 of the leader. Actuation of this carriage movement is produced by the lateral piston and cylinder assembly whose piston rod movements are communicated to the puller plate 88, whose movements in turn are communicated through the braces 90 to the carriage 92.

A mast connecting pin 108 extends forwardly from the front plate 94; and as shown in FIG. 9 this pin is pivotally corrected to the mast 26. The mast is provided with a cross plate 110 having an opening 112 through which the pin 108 extends. A lock ring 114 secures the pin in place in the plate 110 while allowing rotational movement between the two.

In operation of the

crossbeam assemblies

30 and 36 their associated carriages 92 are moved laterally back and forth along the leaders 78. When the carriage movements are together in the same direction, the mast is moved transversely in that direction. However, when the carriages are moved in different amounts or in opposite directions, the mast 26 is rotated or tilted laterally.

It will be noted that when the mast is thus rotated the vertical distance between the upper and lower crossbeam carriage 92 changes although the actual distances between the carriages, along the length of the mast remains the same. This vertical displacement is accomodated by the bracing system which supports the upper crossbeam assembly 36 in such a way that it is held rigidly against lateral and against fore and aft movement while being free to undergo vertical movement. This free vertical movement is achieved by the brace pivot assembly which allows free up and down pivoting of the upper brace assembly 34. It will thus be seen that in the present embodiment the same brace system with free floating upper brace accomodates not only fore and aft rotational movements of the mast but also lateral rotational movements of the mast.

Although a particular embodiment of 'the invention is herein disclosed for purposes of explanation, various modifications thereof, after study of this specification,

will be apparent to those skilled in the art to which the invention pertains.

What is claimed and desired to be secured by letters patent is:

. 1. A mechanism for adjustably supporting a mast from a base member, said mechanism comprising a first mounting means pivotally interconnecting a lower point on said mast in front of a first location of said base member near one edge thereof, a rear brace connected at one end to extend up from a second location on said base member behind said first location, an upper brace freely pivotally connected between. an upper point on said mast and the other end of said rear brace and extendable actuating means for causing forward and rearward movement of said upper brace and pivotal movement of said rear brace with respect to said base, said actuating means being pivotally fastened to said base member between said first and second locations and connected to at least one of said upper and rear braces, the length of said upper and rear braces and the extensibility of said actuating means being sufficient to permit the mast to be retracted to a horizontal transport position on top of said base.

2. A mechanism according to claim 1 wherein said first mounting means comprises a brace extending between and pivotally connected to said lower point on said mast and said first location on said base and a further actuating means for controlling pivotal movements of said first brace with respect to said base member.

3. A mechanism according to claim 2 wherein said further actuating means comprises an hydraulic piston and cylinder assembly extending between a pivot on said base above said first location and a pivot near said lower point on said mast.

4. A mechanism according to claim 1 wherein said actuating means comprises hydraulic piston and cylinder means.

5. A mechanism according to claim 1 wherein said mast is moveable laterally with respect to said first mounting means and said upper brace.

6. A mechanism according to claim 5 wherein crossbeams are connected respectively to said first mounting means and to said upper brace, each crossbeam having a carriage moveable therealong and means pivotally connecting said carriages to said lower and upper points on said mast respectively.

7. A mechanism according to claim 1, wherein said actuating means is connected to a brace pivot assembly which interconnects the upper and rear braces.

8. A mechanism for adjustably supporting a mast from a base member, said mechanism comprising upper and lower generally horizontal crossbeams, a bracing mechanism on said base member and supporting said crossbeams to extend in parallel relationship one above the other, a connector element mounted for movement along the length of each crossbeam, means for separately controlling the movements of said connector elements and pivot means interconnecting said connector elements respectively, to upper and lower locations on said mast for relative pivotal movements about generally horizontal axes perpendicular to said crossbeams, at least one of said pivot means being freely moveable in a vertical direction with respect to said bracing mechanism.

9. A mechanism according to claim 8 wherein actuator means are interconnected between said crossbeams and their respective connector elements;

10. A mechanism according to claim 9 wherein said actuator means comprises hydraulic piston and cylincler means secured to and extending lengthwise of said crossbeams.

11. A mechanism according to claim 10 wherein each connector element is provided with a brace extending therefrom parallel to and beyond the end of the associated crossbeam and means at the end of said brace interconnecting said brace to a moveable portion of the associated hydraulic piston and cylinder means.

12 A mechanism according to claim 8 wherein said bracing mechanism is constructed to maintain said crossbeams rigidly positioned against movement in the fore and aft and lateral directions and the lower crossbeam against movement in the vertical direction while permitting free vertical movement of the upper crossbeam.

13. A mechanism according to claim 8 wherein said pivot means are each fixedly located on said mast.

14. A mechanism according to claim 8 wherein said bracing mechanism includes a generally horizontally extending upper brace pivotally connected at one end to said upper crossbeam and freely pivotally connected at its opposite end to another portion of the bracing mechanism.

15. A mechanism according to claim 8 wherein said crossbeams are formed with rails along their length and wherein said connector elements have rollers fitted to roll along each rail.

Claims

1. A mechanism for adjustably supporting a mast from a base member, said mechanism comprising a first mounting means pivotally interconnecting a lower point on said mast in front of a first location of said base member near one edge thereof, a rear brace connected at one end to extend up from a second location on said base member behind said first location, an upper brace freely pivotally connected between an upper point on said mast and the other end of said rear brace and extendable actuating means for causing forward and rearward movement of said upper brace and pivotal movement of said rear brace with respect to said base, said actuating means being pivotally fastened to said base member between said first and second locations and connected to at least one of said upper and rear braces, the length of said upper and rear braces and the extensibility of said actuating means being sufficient to permit the mast to be retracted to a horizontal transport position on top of said base.

9. A mechanism according to claim 8 wherein actuator means are interconnected between said crossbeams and their respective connector elements.

10. A mechanism according to claim 9 wherein said actuator means comprises hydraulic piston and cylinder means secured to and extending lengthwise of said crossbeams.

12. A mechanism according to claim 8 wherein said bracing mechanism is constructed to maintain said crossbeams rigidly positioned against movement in the fore and aft and lateral directions and the lower crossbeam against movement in the vertical direction while permitting free vertical movement of the upper crossbeam.