WO1991014537A1

WO1991014537A1 - Tool support

Info

Publication number: WO1991014537A1
Application number: PCT/CA1991/000100
Authority: WO
Inventors: Randolph Wallman; Lindsay T. Oliver; James Shewchuk; Mark Rosheim; James Mcneill; David Schaldemose; Mark Friedman
Original assignee: Universal Robotics Corporation; Manitoba Hydro Electric Board
Priority date: 1990-03-27
Filing date: 1991-03-27
Publication date: 1991-10-03
Also published as: AU7544591A

Abstract

A grinding tool support is used in the resurfacing hydraulic turbine blades. The support has a hanger that may be tack welded to the surface of the blade and a telescopic beam that is pivotally connected to the bottom end of the hanger. A load cylinder extends between the hanger and the beam to pivot the beam on the hanger and to vary the load applied to a grinding tool carried by one end of the beam. The load cylinder and a beam extending mechanism are under the control of the operator through the use of controls at the grinder. This alleviates the operator of the heavy loads imposed in overhead grinding under awkward conditions.

Description

TOOL SUPPORT

FIELD OF THE INVENTION

The present invention relates to a tool support and has particular application to supporting a surface working tool/ such as a grinder, for working large surfaces.

BACKGROUND OF THE INVENTION

It is often necessary to work large metal surfaces under awkward conditions. For example, the draft tubes and turbine blades used in hydroelectric generating stations require periodic maintenance to repair cavitation damage. This involves welding the damaged surface to build up pitted areas and grinding the surface to its original contour. This work is usually done with the workpiece in situ. The work is performed manually, with all of the effort required to support the tool and to traverse it over the surface being exerted by the operator. This is extremely tiresome and, in many cases, difficult to perform because of the location and orientation of the surface being worked. The objective of the present invention is to provide a means for supporting a tool and applying the working force during work of this sort.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a tool support for supporting a tool as the tool is being used on a workpiece, the support comprising: an elongate, extensible beam; tool holder means on the beam for mounting a tool thereon; beam hanger means connected to the beam at a position spaced from the tool holder means for mounting the beam on a workpiece, the hanger means comprising a stationary component for mounting on the workpiece

SUBSTITUTE SHEET and a movable component connected to the beam and movably mounted on the first component; beam extending means for control of the extending beam; and tool biasing means for urging a tool carried by the tool holder against the workpiece. The tool can thus be moved over the surface, supported by the support, with minimal effort on the part of the operator. In preferred embodiments of the invention, the tool holder includes a swivel mounting, for example a spherical bearing, with the tool balanced on the centre of the mounting, thus allowing the orientation of the tool to be varied while minimizing the amount of effort that is required of the operator to balance the tool in use.

The beam hanger preferably includes a rotary coupling, allowing the beam to turn about an axis generally normal to the surface being worked. This allows the tool to sweep over the surface as well as to move along the surface with the extension and retraction of the beam. The hanger may also, or alternatively, include a rail unit mounted on the surface and a carriage for transporting the beam along the rail unit.

The tool biasing means preferably acts by pivoting the beam around an axis transverse to the beam and transverse to the sweep axis.

According to another aspect of the present invention there is provided a grinding tool for grinding a surface comprising: a hanger including: a base adapted to be fixed to the surface to be ground; a shaft mounted on the base for rotation about a first axis; shaft drive means for controllably rotating the

SUBSTITUTE SHEET shaft on the base; a rotor mounted on the shaft for rotation about the first axis; clutch means for selectively engaging the rotor with the shaft to rotate therewith; and pivot means mounted on the rotor; a beam pivotally mounted on the pivot means for pivotal movement about a second axis transverse to the first axis; beam pivoting means extending between the hanger and the beam for pivoting the beam about the second axis; tool holder means mounted on the beam at a position remote from the pivot means; and control means adjacent the tool holder means for controlling operation of the shaft drive means and the beam pivoting means. The sweep motion of the tool is thus controlled, and the tool pressure against the surface to be worked is supplied by the tool support not the operator.

According to another aspect of the present invention there is provided a grinding tool for grinding surface comprising: a hanger including: a base adapted to be fixed to the surface to be ground; a shaft; a rotatable, quick-release coupling having a first component carried by the base and a second component carried by the shaft; lock means having a first lock component carried by the base and a second lock component carried by the shaft, the second lock component being operatively engageable with the first lock

SUBSTITUTE SHEET component in a plurality of angular positions of the shaft with respect to the base, so as to prevent rotation of the shaft with respect to the base, spring means normally engaing the second lock component with the fist lock component and power operated release means for selectively releasing ' the second lock component from the first lock component; a beam comprising: an outer box beam pivotally mounted on the pivot means intermediate the ends of the box beam; an inner beam extending along the inside of the outer beam; inner beam support means within the outer beam supporting the inner beam for movement therealong such that the inner beam may be extended telescopically from one end of the outer beam; power operated beam extension means within the outer beam for extending and retracting the inner beam telescopically with respect to the outer beam; beam pivoting means extending between the shaft and the outer beam for pivoting the beam on the pivot means; a grinding tool mounted on an end of the inner beam for universal rotation thereon; control means located adjacent the grinding tool for selectively and independantly controlling operation of the grinding tool, the beam extension means and the beam pivoting means, said control means including means operatively connected to the power release means of the pedestal lock means for releasing the lock

SUBSTITUTE SHEET means in response to actuation of the grinding tool. In use, the hanger may be tack welded to the surface to be finished. The beam at least partially balances the weight of the tool, while the beam pivoting means, usually a pneumatic cylinder, is used to apply the force on the tool necessary to grind the surface. The beam may pivot on the hanger and may be extended under power so that the grinding work can cover a large surface of the blade surface with a single setup of the tool support.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which illustrate an exemplary embodiment of the present invention:

Figure 1 is a side elevation of a tool support according to the present invention;

Figure 2 is a side elevation, partially in section of a hanger;

Figure 3 is an end view of a hanger base component;

Figure 4 is a side view of a hanger coupling component;

Figure 5 is an end view of the hanger coupling component;

Figure 6 is a transverse cross section of the beam along line 6-6 of Figure 1;

Figure 7 is a longitudinal cross section of the beam along line 7-7 of Figure 6;

Figure 8 is an elevation, partially in section of a tool holder;

Figure 9 is a schematic of a control circuit for the tool support;

Figure 10 is a cross section of an alternative embodiment of a hanger;

Figure 11 is an end view of the spigot of the hanger

SUBSTITUTE SHEET of Figure 10;

Figure 12 is a partial plan view of a tool support mounted on a rail unit; and

Figure 13 is a section along line 13-13 of Figure 12.

DETAILED DESCRIPTION

Referring to the accompanying drawings and especially to Figure 1, there is illustrated a tool support 10 for a grinding tool 12. The support includes a hanger 14 pivotally connected at one end to a beam 16 and mounted at the other end on a workpiece 17. At one end of the beam an offset support arm 18 supports the grinder 12. A load cylinder 20 is connected at the cylinder end to a pair of lugs 22 mounted on the beam 16 adjacent the end opposite the grinder 12. The opposite end of the load cylinder is connected to an offset arm 24 extending from the hanger 14. The beam is thus supported by a hanger a first class lever with the pneumatic load cylinder 20 serving to control the pivoting of the beam about the fulcrum.

The hanger construction is most clearly illustrated in Figures 2 through 5. The hanger includes a base component 26 and a hanger coupling component 28. The base component includes a mounting plate 30 (Figure 1) that is mounted directly on a surface to the work by the tool. An annular housing 32 is carried by the mounting plate. As illustrated in Figure 2, the housing has an internal shoulder 34 supporting a bearing 36, held in place by a retainer 38. The bearing supports a shaft 40 with a shoulder 42 engaging one end of the bearing 36. The bearing is retained in place on the shaft by engagement with a hub 44 of a worm gear 46 within the housing 32. The worm gear is driven by a worm 48 extending across the housing and driven by a motor 50 (Figure 1).

The shaft 40 projects from the housing 32. It is

SUBSTITUTE SHEET formed with a shoulder 52 that supports a bearing 54. A retainer 56 on the end of the shaft holds the bearing in place. Surrounding the bearing and projecting beyond the end of the shaft 40 is an annular rotor 58. The rotor has an inside shoulder 60 and a retainer 62 that secures the rotor in place on the bearing. At its outermost end, the rotor 58 has a annular flange 64.

Between the rotor 58 and the annular housing 32, the shaft 40 has an annular flange 66. This serves to support a clutch 68 for engaging the shaft and the rotor. As illustrated in Figure 2, the clutch includes an annular channel 70 secured to the flange 66 of the shaft 40. The channel opens outwardly with its web confronting an outer cylindrical surface 71 on the rotor 58. Mounted on the inside of the web of the channel 70, confronting the rotor surface 71 is an annular bladder 72 that may be inflated to engage the surface 71 of the rotor so that the shaft and the rotor will turn as a unit.

The coupling component 28 of the hanger is fastened to the rotor 40 using a bayonet coupling 74. This includes a cylindrical socket 76 in the end of the rotor that is partially covered by an annular plate 78 with three segmental lugs 80 spaced uniformly about the inside of the plate and projecting over the socket. The coupling is provided with a lock 82 positioned between two adjacent lugs 80 and sliding into a recess 84 in the base of the socket 76. The lock is biased out of the socket by a spring 86 in the recess. As illustrated most particularly in Figure 3, the lock is shaped as a ring segment, matching the space between the adjacent lugs 80. A release lever 88 is secured to the lock 82 and projects to the outside of the rotor 58 through an appropriate slot (not shown).

The coupling component 28 of the hanger has a main flange 90 that matches the configuration of the rotor flange

SUBSTITUTE SHEET 64. In the engaged position, these two flanges engage face to face. A shaft 92 projects from the flange 90. It has an annular groove 94 adjacent the flange and three cut-away segments beyond the groove to provide three lugs 96 that match the spaces between the lugs in the plate 78.

To assemble the two components of the hanger, the coupling component is placed on the base component so that the lugs 80 and 96 will mesh. One of the lugs 96 will then depress the lock 82 as the two components are brought together. When the flanges 64 and 90 come into engagement, the two components may be rotated until the lock 82 is released, at which time the lugs 96 are located beneath the lugs 80 and the lock 82 prevents further relative rotation of the two hanger components until the release lever 88 is depressed.

The bayonet coupling is used as a quick-release mechanism for mounting the beam and related components on the base component 14 of the hanger simply by presenting the beam to the hanger base component and turning slightly. For operation, it is desired to install three bolts 98 fastening the flange 90 to the flange 64 somewhat more securely.

On the side of flange 90 opposite the shaft 92 are two lugs 100 that are fastened to the offset arm 24 with two bolts 102 and mating nuts 104.

The configuration of the beam 16 is most clearly illustrated in Figures 6 and 7. The beam includes a box section housing 106 with a handle 108 at one end. The handle is recessed at 110 so that the sides of the box section 106 can be seated against the appropriate shoulders on the handle and fastened in place. The handle 108 has a handle opening 112 which is used for carrying and manipulating the beam. The opposite end of the box section 106 is fastened to a handle 114 using a similar recess 116. The handle 114 also has a handle opening (not shown).

SUBSTITUTE SHEET As illustrated in Figure 7, a plate 120 extends across the interior of the housing 106 at a position spaced somewhat from the handle 108. The plate carries an air motor 122 driving a lead screw 124 extending the length of the housing 106. The end of the lead screw adjacent the handle 114 is supported in a bearing 126.

The lead screw drives a re-circulating ball nut 128 that is mounted on an inner beam section 130. The beam section 130 is a plate supported for longitudinal sliding movement in an outer beam section 132. The outer beam section includes a plate 134 and two L-shaped caps 136 fastened to opposite edges of the plate by cap screws 138. The outer beam section 132 is itself mounted in the housing 106 by two C-shaped supports 140 which allow the outer beam section to slide longitudinally within the housing 106.

As illustrated in Figure 7, one of the caps 136 has a groove 142 extending partway along its length. This receives a block 144 mounted on the inner beam section 130 so that as the inner beam section 130 is driven out from the end of the box section 106 by operation of the motor 22 and lead screw 24, the block 144 engages the end of the groove 142 and draws the outer beam section 132 out of the beam as well. This two stage extension of the beam allows an overall smaller length of the section 106 than would otherwise be the case.

The handle 108 closes off the adjacent end of the housing 106, while the handle 114 has an opening sufficient to accommodate the beam sections 130 and 132 as they slide from the housing 106. The handle 114 also has a recess 146 to accommodate an end plate supporting the bearing 126.

As illustrated most particularly in Figure 1, a boot 148 is connected at one end to the housing 106 and at the other to the inner beam section 130 to close the end of the beam against the ingress of contaminants.

Figure 8 illustrates the tool holder 150 that is used

SUBSTITUTE SHEET to provide a balanced mounting of the grinder 14 on the end of the mean 16. The tool holder includes a ring 152 mounted on the end of the tool arm 18. The ring serves as the support for a spherical bearing 154 with the outer shell 156 seated in the ring. The outer shell has an inner part spherical surface 158. The inner shell 160 of the bearing has an outer part spherical surface 162 that mates with the surface 158. The inner shell 160 of the bearing is supported on a sleeve 164 and abuts a shoulder 166 on the sleeve. The inner shell is held in place by a collar 168 threaded onto the end of the sleeve. At one end, the sleeve 164 is provided with an internal shoulder 170 that supports a set of bearings 172, for example tapered roller bearings to accommodate thrust loadings. The bearings in turn support a shaft 174 extending through the housing. A nut 176 and a bearing retaining washer 177 are fitted on the threaded end 178 of the shaft 174 to retain the bearings in place.

At the opposite end of the shaft 174, within the sleeve 164, is a coupling 180 keyed to the shaft. The coupling threads onto the threaded drive shaft 182 of a grinder motor 184. The collar 168 has an annular flange 186 that is fastened to the motor using a set of machine screws 188.

On the end of sleeve 164 opposite the collar 168 is an annular flange 190 that supports a transparent shield 192, fastened in place using bolts 194 and nuts 196.

The tool support and the grinder are operated pneumatically using the system illustrated in Figure 9. As illustrated in that Figure, an air supply line 198 leads to a valve 197 and to grinder 12. The exhaust from the grinder is bled off through a line 199 leads to a three-position valve 200 for controlling operation of the single end pneumatic load cylinder 20. The valve supplies air to the cylinder through a pressure control 201 and a variable restrictor 202

SUBSTITUTE SHEET. so that the movements of the cylinder will be smooth and not jerky.

The valve 200 is operated by air delivered through pilot lines 204 connected to a pilot valve 206 located at the grinding tool 12.

The beam extension motor 122 is controlled by a three position valve 208 supplied with air from an air supply line 209 through a pressure control 211 and a variable restrictor 210. The valve is in turn controlled by air through two pilot lines 212 from a selector valve 213 and a pilot valve 214 at the grinder.

The beam swing motor 50 is controlled by a three- position valve 216 supplied with air through a pressure control 217 and a variable restrictor 218. The pilot lines 220 connected to valve 216 lead to the selector valve 213 that may be used to connect the valve 214 either to the pilot lines 212 for the beam extension motor or to the pilot lines 220 for the beam swing motor 50. This arrangement is used to limit the number of controls at the grinder. Where desired, separate controls can be provided.

The clutch 68 is operated at the same time as the swing motor using two air lines 224. Where desired, an additional clutch control can be provided for engaging the clutch as a brake when the motor 50 is not being operated.

The grinder 12 is operated using the valve 197 to supply with air from the air supply line 198. Downstream of the valve 197 are pressure control 226 and a variable restrictor 228 which supply reduced pressure air for operating the pilot valves 206 and 214.

With this arrangement of valves, the operator has accessible at the grinding tool all the necessary controls to allow the positioning of the tool as desired over a wide area of surface to be worked. The operator can control the pressure applied through the use of the load cylinder 20.

SUBSTITUTE SHEET Because the load cylinder is supplied from the exhaust of the grinder motor, it will only be active when the grinder is operating.

An alternative embodiment of the hanger is illustrated in Figures 10 and 11 of the accompanying drawings. The illustrated alternative hanger 229 includes a quick-release coupling 230. This has a base component 232 with a base flange 234 and a spigot 236 projecting from the base flange. In the end face of the spigot, opposite the flange is a multi-point socket 238 of the type used to engage hexagonal bolt heads and nuts. An annular groove 240 surrounds the spigot 236 and its outer edge is chamfered at 242. The other component of the quick-release coupling includes a collar 244 that slides onto the end of the spigot 234. The collar has a series of fingers 246 with internal grooves 248 near their outer ends to engage the outside of a split ring 250.

A lock ring 252 slides on the collar 244 and normally engages the outside of the fingers 246 to retain them in engagement with the split ring 250, which is also seated in the groove 240 in the spigot. The lock ring 252 may be drawn over the collar against the force of an internal coil spring 254 until a lug 255 comes into alignment with a groove 256 in the fingers. This allows the fingers to move outwardly, allowing the split ring 250 to be cammed out of the groove 240, thus releasing the coupling.

The collar 244 has a hexagonal end 257 that is internally threaded at 258 to engage on the end of a sleeve 260 forming part of a composite shaft 262. The sleeve 260 has an internal annular end flange 264 on the end opposite the collar 244 and a peripheral external flange 266 that is located at the end of the collar. Within the sleeve 260 is a hard rubber sleeve 268 with an internal, hexagonal shape for reasons that will be described more fully in the following.

SUBSTITUTE SHEET Extending from the flange 266 is a cylindrical housing 280 with an end flange 282 coupled to the flange 266 by cap screws 284. The end 286 of the housing carries a pair of spaced apart lugs 288.

Within the housing 280 is a pneumatic cylinder 290 that has an internal spring 292 normally driving the piston 294 in a direction that will extend the rod 296 from the cylinder. At the rod end of the cylinder 290 is a threaded sleeve 298 threaded into the centre of the end flange 264 of sleeve 260.

The outer end of the piston rod 296 is fixed to a hexagonal key 300 that slides in the similarly shaped rubber sleeve 268 and is normally projected into engagement with the socket 238 in the spigot 236 through action of the spring 292. The application of air pressure to the cylinder 290 compresses the spring and withdraws the key 300 from the socket 238. Thus, the key 300 serves as a lock normally locking the housing 280 to the spigot 238 so that the two will not rotate. Rotation is only possible when the cylinder 290 is being actuated to compress spring 292. The rubber sleeve 268 acts as a shock absorber to limit shock loadings produced by the sudden engagement of the key 300 in the socket during rotation of the housing. The lugs 288 on the end of the housing are connected to the beam as the fulcrum point. Two additional lugs 302 carried by the housing 280 are connected to the rod end of the cylinder 20 by pin 304.

Rather than mounting the hanger directly on the surface to be worked using a tack welded mounting plate 30 or a base flange 234, the hanger may include a rail unit 306 illustrated most particularly in Figures 12 and 13. The rail unit has two end housings 308 to be tack welded to the surface to be worked. Two cylindrical rails 310 extend between the two end housings. They are supported on pedestals 312. A lead screw 314 also extends between the end

SUBSTITUTE SHEET housings. It is located below and between the rails 310. The rails support a carriage 316 on which the housing 32 of the hanger is mounted. The carriage is supported on the two rails using four rail followers 318, each of which is a partial sleeve surrounding the associated rail. A nut 320 on the lead screw 314 serves to drive the carriage 316 along the rails when the lead screw is rotated by a motor 322 in one of the end unit housings 308. As illustrated most particularly in Figure 13, the rail unit is mounted in a channel 324 with a base web 326 and two side flanges 328. Each of the flanges 328 extends to a position above the rails. The flanges have opposed grooves 330 on the inside to receive opposite edges of a sliding curtain 332. Two curtains are provided, attached to opposite ends of the carriage 316. Each curtain is wound on a spring loaded roller 344 mounted on a respective one of the end units 308. As the carriage is advanced along the rails, one of the curtains will be wound onto the respective rollers 334, while the other will be drawn out. This encloses the top of the channel to prevent undue contamination of the rail unit.

While particular embodiments of the invention has been described in the foregoing, it is to be understood that other embodiments are possible within the scope of the invention. The invention is to be considered limited solely by the scope of the appended claims.

SUBSTITUTE SHEET

Claims

(1) A tool support for supporting a tool as the tool is being used on a workpiece, the support comprising: an elongate, extensible beam; tool holder means on the beam for mounting a tool thereon; beam hanger means connected to the beam at a position spaced from the tool holder means for mounting the beam on a workpiece, the hanger means comprising a stationary component for mounting on the workpiece and a movable component connected to the beam and movably mounted on the first component; beam extending means for control of the extending beam; and tool biasing means for urging a tool carried by the tool holder against the workpiece.

(2) A tool support according to claim 1 wherein the tool holder means comprise swivel means allowing variable orientation of a tool with respect to the beam.

(3) A tool support according to claim 2 wherein the swivel means comprise a spherical bearing with an outer component mounted on the beam and an inner component adapted to be mounted on the tool.

(4) A tool support according to claim 1 wherein the stationary component of the hanger means comprises elongate rail means, and the movable component comprises a carriage movable along the rail means.

(5) A tool support according to claim 4 wherein the carriage comprises rotary coupling means permitting rotation of the beam about a first sweep axis transverse to the beam and transverse to the rail means.

(6) A tool support according to claim 5 wherein the carriage comprises pivot means mounting the beam for pivotal movement about a second axis transverse to the beam and

SUBSTITUTE SHEET transverse to the first axis.

(7) A tool support according to claim 6 wherein the tool biasing means comprise means for pivoting the beam about the second axis.

(8) A tool support for supporting a tool for use on a workpiece, the support comprising: an elongate, longitudinally extensible beam; tool holder means carried by the beam; hanger means coupled to the beam at a position spaced from the tool holder means for mounting the beam on a surface of the workpiece, the hanger means including a rotary coupling means permitting rotation of the beam about a first axis to sweep the tool holder means over the work piece and beam pivot means permitting pivotal movement of the beam about a second axis transverse to the first axis to move the tool holder towards and away from the workpiece; beam pivoting means for pivoting the beam about the second axis; beam extension means for controllably extending and retracting the beam between the hanger and the tool support means; and control means for selectively controlling operation of the beam pivoting means and the beam extension means.

(9) A tool support according to claim 8 wherein the control means comprise operator actuable controls adjacent the tool holder means.

(10) A tool support according to claim 9 wherein the control means include a first control for controlling operation of the beam pivoting means and a second control for controlling operation of the beam extension means.

(11) A tool support according to claim 10 including

SUBSTITUTE SHEET beam sweep means for controllably rotating the beam about the first axis.

(12) A tool support according to claim 11 wherein the control means further include means for selectively actuating the second control for alternatively controlling operation of the beam extension means and the beam sweep means.

(13) A tool support according to claim 12 including clutch means for selectively engaging and disengaging the beam sweep means.

(14) A tool support according to claim 8 wherein the beam comprises at least two beam sections longitudinally movable with respect to one another.

(15) A tool support according to claim 14 wherein the beam comprises an outer housing and at least one extendible beam section mounted within the housing.

(16) A tool support according to claim 8 wherein the hanger means comprise a rotatable quick-release coupling with separable first and second components, the first component being mountable on the workpiece and the second component being mounted on the beam.

(17) A tool support according to claim 16 including lock means for selectively preventing rotation of the rotary coupling.

(18) A tool support according to claim 17 including lock operating means comprising means for disengaging the lock in response to actuation of a tool carried by the tool holder means.

(19) A grinding tool for grinding a surface comprising: a hanger including: a base adapted to be fixed to the surface to be ground; a shaft mounted on the base for rotation about a first axis;

SUBSTITUTE SHEET shaft drive means for controllably rotating the shaft on the base; a rotor mounted on the shaft for rotation about the first axis; clutch means for selectively engaging the rotor with the shaft to rotate therewith; and pivot means mounted on the rotor; a beam pivotally mounted on the pivot means for pivotal movement about a second axis transverse to the first axis; beam pivoting means extending between the hanger and the beam for pivoting the beam about the second axis; tool holder means mounted on the beam at a position remote from the pivot means; and control means adjacent the tool holder means for controlling operation of the shaft drive means and the beam pivoting means.

(20) A tool holder according to claim 19 wherein the beam comprises a plurality of beam components movable longitudinally with respect to one another to extend and contract the beam.

(21) A tool holder according to claim 20 including beam extension means for extending and contracting beam.

(22) A tool support according to claim 21 wherein the control means comprise means for selectively operating the beam extension means.

(23) A grinding tool for grinding surface comprising: a hanger including: a base adapted to be fixed to the surface to be ground; a shaft; a rotatable, quick-release coupling having a first component carried by the base and a second

SUBSTITUTE SHEET component carried by the shaft; lock means having a first lock component carried by the base and a second lock component carried by the shaft, the second lock component being operatively engageable with the first lock component in a plurality of angular positions of the shaft with respect to the base, so as to prevent rotation of the shaft with respect to the base, spring means normally engaing the second lock component with the fist lock component and power operated release means for selectively releasing the second lock component from the first lock component; a beam comprising: an outer box beam pivotally mounted on the pivot means intermediate the ends of the box beam; an inner beam extending along the inside of the outer beam; inner beam support means within the outer beam supporting the inner beam for movement therealong such that the inner beam may be extended telescopically from one end of the outer beam; power operated beam extension means within the outer beam for extending and retracting the inner beam telescopically with respect to the outer beam; beam pivoting means extending between the shaft and the outer beam for pivoting the beam on the pivot means; a grinding tool mounted on an end of the inner beam for universal rotation thereon; control means located adjacent the grinding tool for selectively and independantly controlling

SUBSTITUTE SHEET operation of the grinding tool, the beam extension means and the beam pivoting means, said control means including means operatively connected to the power release means of the pedestal lock means for releasing the lock means in response to actuation of the grinding tool.

SUBSTITUTE SHEET