Metal working machine

Aug. 5, 1958

2,845,751

W. M. WOODWARD

METAL WORKING MACHINE

<img file="US2845751A_D0001.tif" />

W. M. WOODWARD

METAL WORKING MACHINE

Aug. 5, 1958

Filed Jan. 10, 1955

2,845,751

Sheets-Sheet 2

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Aug. 5, 1958

2,845,751

W. M. WOODWARD

METAL WORKING MACHINE

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ATTOMFVS

Aug. 5, 1958

2,845,751

VJ. M. WOODWARD

METAL WORKING MACHINE

Filed Jan. 10, 1955

Sheets-Sheet 4

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Aug. 5, 1958

2,845,751

W. M. WOODWARD

METAL WORKING MACHINE

Filed Jan. 10, 1955

Sheets-Sheet 5

<img file="US2845751A_D0005.tif" />

<img file="US2845751A_D0006.tif" />

W. M. WOODWARD

METAL WORKING MACHINE

Aug. 5, 1958

Filed Jan. 10, 1955

2,845,751

Sheets-Sheet 6

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<img file="US2845751A_D0008.tif" />

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Aug. 5, 1958

W. M. WOODWARD

2,845,751

METAL WORKING MACHINE

Filed Jan. 10, 1955

Sheets-Sheet 7

<img file="US2845751A_D0010.tif" />

A97TORNEYS

Aug. 5, 1958

W. M. WOODWARD

2,845,751 'METAL WORKING MACHINE

Filed Jan. 10, 1955

Sheets-Sheet 8

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INVENTOR.

William M. Wmlmalpd by

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W. M. WOODWARD

METAL WORKING MACHINE

Aug. 5, 1958

Filed Jan. 10, 1955

2,845,751

Sheets-Sheet 9

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Aug. 5, 1958

2,845,751

W. M. WOODWARD

METAL WORKING MACHINE

Filed Jan. 10, 1955

Sheets-Sheet 10

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W/LL/AM M. WOODWMD

BY

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United States Patent Office

2,845,751

Patented Aug. 5, 1958

2,845,751 METAL WORKING MACHINE

William M. Woodward, Birmingham, Mich., assignor to Mid-West Abrasive Company, Owosso, Mich., a corporation of Delaware

Application January 10, 1955, Serial No. 480,661 22 Claims. (Cl. 51—32)

This invention relates to a metal working machine and more particularly to a swing grinder of the type commonly used for grinding metal billets of substantial length.

One object of this invention is to provide a grinding machine having a carriage movable along a track and a boom mounted on the carriage with an abrasive wheel rotatably mounted on the free end of the boom. The boom is supported by the carriage for vertical swinging movement and is slidable along its longtudinal axis to feed the abrasive wheel across a work piece. The boom is also rotatable in opposite directions about its longitudinal axis to tilt the abrasive wheel in opposite directions.

Another object of the invention is to provide a construction wherein the abrasive wheel is automatically tilted in opposite directions during the grinding operation to maintain the wheel in a properly dressed condition.

Still another object of the invention is to provide counterbalancing means for the boom and associated parts including the brasive wheel, movable in opposed relation to the in and out axial sliding movement of the boom.

Still another object of the invention is to provide a variable pull down device for maintaining a predetermined downward pull upon the outer end of the boom which varies in accordance with the axial in and out movement of the boom. It is necessary to maintain a uniform grinding pressure of the wheel upon the work piece as it moves back and forth across the work piece. However, it has been found to be very difficult if not impossible to accurately counterbalance the boom with weights alone. Accordingly, the pull down device of the present invention cooperates with the counterbalancing means to provide a uniform grinding pressure as the wheel moves back and forth across the work.

It has also been found that under operating conditions the engagement of the grinding wheel with the work piece has a tendency to cause the wheel to chatter and the boom to vibrate in a vertical plane, particularly in the outermost position of the boom, if the boom is not subjected to sufficient hold down pressure. Although the boom may be counterbalanced in a manner to be slightly tool heavy, still there is this tendency toward chattering where there is no positive or nearly positive resistance to upward swinging of the tool end of the boom. This can be appreciated when one pictures a rather massive boom more or less in balance with respect to the pivot ⁶⁰axis. Clearly there is no positive resistance to vertical rocking. The pull down device of the present invention is in the form of a hydraulic fluid pressure operated piston cylinder assembly and adds a certain amount of downward pull on the tool end of the boom. In addition to the actual pull down pressure thus applied, the hydraulic fluid in the pull down assembly provides a much greater positive resistance against upward swinging of the boom. Even pneumatic pressure is useful for this purpose although it does not provide a resistance to chattering of the effectiveness of hydraulic fluid.

Other objects of the invention will become apparent as the following description proceeds, especially when taken in conjunction with the accompanying drawings wherein:

Figure 1 is a top plan view of a metal working machine 5 constructed in accordance with the present invention;

Figure 2 is a side elevational view of the machine shown in Figure 1;

Figure 3 is a sectional view taken along the line 3—3 on Figure 1;

¹⁰ Figure 4 is a sectional view taken along the line 4—4 on Figure 3;

Figure 5 is a sectional view taken along the line 5—5 on Figure 1;

Figure 6 is a sectional view taken along the line 6—6 ¹⁵ on Figure 3;

Figure 7 is a sectional view taken along the line 7—7 on Figure 1;

Figure 8 is a front elevational view of the machine partly in section;

²⁰ Figure 9 is a plan view of a portion of the boom, showing also the means connecting to the boom the motor for driving the abrasive wheel for in and out axial sliding movement as a unit with the boom;

Figure 10 is an enlarged view partly in section of a ²⁸ portion of the structure shown in Figure 9;

Figure 11 is an enlarged view partly in section of another portion of the structure shown in Figure 9;

Figure 12 is a sectional view illustrating the counterbalancing means for the boom;

³⁰ Figure 13 is a sectional view taken along the line 13—13 on Figure 1;

Figure 14 is a sectional view taken along the line 14—14 on Figure 3;

Figure 15 is a diagrammatic view of the hydraulic ^dt} system; and

Figure 16 is a detail view of the pressure regulating valve.

The metal removing machine selected for the purpose of illustrating the present invention is adapted to remove ⁴⁸ metal by an abrading action and comprises a swing grinder.

Referring now more particularly to the drawings and especially to Figures 2, 3 and 8, it will be noted that the swing grinder has a supporting structure which includes a track 10 and a carriage 12 supported thereon for movement in opposite directions along the track. The track comprises laterally spaced rails 14 and 16 suitable anchored to flooring or other supporting means not shown 50 h^ere'ⁿ' The rail 14 is generally l-shaped in cross section and the rail 16 has an inverted channel-shaped cross section.

The numeral 18 designates a work support for a work piece W to be operated upon by the machine. In the pres55 ^ent '^nstance&gt; the work piece may be considered as a metal billet of a substantial length, and it is the purpose of this machine to remove metal from the top surface of the billet. The track extends in the general direction of length of the billet so that the machine may move lengthwise of the billet during the grinding operation.

The carriage includes a rectangular platform 20 having downwardly extending flanges 22 at the front and rear ends of the platform, and the wheel supporting axles 24 and 26 are respectively journalled in the flanges 22.

These axles extend from front to rear of the carriage and have wheels 28 and 30 keyed or otherwise secured to the opposite end portions of the axles in positions to engage the rails 14 and 16.

It will be noted that the wheels 28 which engage the 70 .⁴⁴ have a circumferentially grooved periphery for engaging the track and guiding movement of the carriage therealong.

In the present instance, the carriage is driven in op2,845,751 posite directions along the track by a reversible fluid motor 32 of any suitable construction secured to the platform 20 of the carriage. The drive shaft of the motor is connected to a gear box 34 which has a sprocket 36 connected by a chain 38 to a sprocket 40 on the axle 24 to move the carriage in opposite directions along the track.

The fluid motor 32 is driven in a manner more fully described hereinafter. Briefly, as shown in Figure 15 of the drawings, the motor 32 is connected to fluid pressure supplied by a duplex pump assembly 37 and is selectively operated by a suitable four-way three position valve 39. The valve 39 is supported on the frame structure and is controlled by a lever 41.

The numeral 42 indicates a boom assembly which is mounted on the carriage 12 and which extends outwardly from the carriage at right angles to the track 10 over the top of the work piece W, as shown in Figure 3 of the drawings. The boom assembly 42 includes an elongated boom tube 44 supported on the carriage in a manner more fully described hereinafter and having an abrasive wheel assembly 46 mounted on the outer end thereof.

The abrasive wheel assembly 46 is shown in Figure 10 of the drawings as having a housing 48 formed with a circular recess 50 in the inner end wall thereof for receiving the outer end of the boom tube 44. The outer end of the boom tube is secured in the recess in any suitable manner and accordingly the abrasive wheel assembly is movable as a unit with the boom tube. One side of the housing 48 is open and is normally closed by a cover 52 having the inner edge pivoted to the housing by a pin 54 in a manner to permit outward swinging movement of the cover relative to the housing.

The wall 56 of the housing 48 opposite to the cover 52 is fashioned to support a spindle 58 with its axis extending at right angles to the axis of the boom tube 44. In detail, the wall 56 of the housing is fashioned with a sleeve part 60 for receiving one end of the spindle 58 and the latter is secured to the sleeve part by a key 62. The spindle 58 extends from the sleeve part axially through housing 48 and the central portion of cover 52 is apertured to receive the free end of the spindle. It will be noted from Figure 10 that the free end of the spindle is threaded and the central portion of cover 52 is clamped to the spindle by a nut 64. A pulley 66 is journalled on spindle 58 by a roller bearing 68 and the periphery of the pulley is formed with axially spaced annular belt receiving grooves 70. The end of the pulley opposite the grooved end is secured by studs 72 to the adjacent end of a ring 74 having a reduced part concentric to the spindle 58 and journalled on the spindle by a roller bearing 76.

An abrasive wheel 78 is sleeved on the reduced portion of ring 74 and is seated against the shoulder 80 formed by the reduced portion of the ring. The abrasive wheel 78 is secured in place on the ring by an annular nut 82 which is threaded on the end of ring 74. An annular spacer 84 is supported on the ring between nut 82 and the abrasive wheel 78. With the above construction, the spindle 58 and associated parts may be readily installed or replaced when desired. The abrasive wheel may be replaced by merely swinging cover 52 to its open position and removing the clamping nut 82. As seen in Figure 3 of the drawings, the bottom of the housing 48 is open and the abrasive wheel 78 projects therebeneath for engagement with the work piece.

The abrasive wheel 78 is rotated by an electric motor 86 mounted on a carriage 88 which, in turn, is supported by a track 90 having laterally spaced rails 92 extending parallel to the axis of the boom tube 44. As shown particularly in Figure 8, the carriage is equipped with axles 94 having rollers 95 positioned at opposite ends thereof for rolling engagement with the respective rails 92. The carriage 88 is held in position on the track 90 by suitable brackets 96 secured to opposite sides of the carriage and 'having rollers 98 at the lower ends thereof respectively engageable with the bottom sides of rails 92. Thus, the carriage 88 with the motor 86 thereon is movable in the direction of the boom axis and at right angles to the track between the broken and full line positions shown in

Figures 1 and 2 of the drawings.

The drive shaft of the electric motor 86 is connected to a gear box generally indicated at 100 suitably mounted on the carriage 88, and a pulley 102 is secured to the output shaft of the gear box. The pulley 102 has axially spaced grooves extending about the periphery thereof for receiving the inner ends of belts 104. The outer ends of the belts 104 are respectively received in the grooves 70 of the pulley 66 so that rotation of the motor 86 imparts a rotative movement to the abrasive wheel 78.

As will be described more fully hereinafter, the boom tube 44 is movable in opposite directions along its longitudinal axis in order to feed the abrasive wheel 78 back and forth across the work piece W. The carriage 88 is movable as a unit with the boom tube 44 during the feeding traverse of the abrasive wheel. In order to accomplish this result, a tie rod assembly 106 is provided between the carriage 88 and the abrasive wheel housing 48. The tie rod assembly 106 comprises a plurality of axially aligned relatively movable parts and performs the additional functions of maintaining the belts 104 under the proper tension.

Referring now to Figure 11 of the drawings, it will be noted that the tie rod assembly 106 has a pair of central rod sections 108 suitably fashioned at the adjacent ends to overlie and interlock with one another. The rod sections 108 are held in their assembled relationship by a sleeve 110 normally extending over the joint between the overlying rod sections and frictionally held by a detent 112 against a stop in the form of a tapered pin 114. The sleeve 110 is movable axially of the tie rod assembly 106 in a direction away from stop 114 to enable disengaging the adjacent ends of rod sections 108 and thereby to permit replacing belts 104 when desired.

The axially outer ends of rod sections 108 are formed with recesses 116 for respectively receiving the inner ends of coil springs 118. The axially outer end of one of the coil springs 118 extends into a recess 120 formed in a part 122 which is secured to a bracket 124 rigidly carried by the gear box 100 on the carriage 88. The outer end of other coil spring 118 extends into a recess 126 formed in the axially inner end of a part 128. The axially outer end 129 of the part 128 is externally threaded and projects into a bore 130 formed in the housing 48. The bore 130 loosely receives the threaded end 129 of part 128 and a key (not shown) is employed to prevent relative rotation between the end 129 and bore 130.

In order to axially move the part 128 to adjust the tension on belts 104, a feed nut 132 is threaded to the part 129 and is arranged to mesh with a worm 134 suitably journalled in the housing 48. The arrangement is such that rotation of worm 134 imparts a rotative movement to the feed nut 132 which, in turn, axially shifts the threaded part 128 to effect the desired adjustment.

The parts 122 and 128 are respectively encircled by coil springs 136 having the convolutions adjacent the outer ends respectively engaged in helical grooves formed in the aforesaid parts and having the convolutions adjacent the inner ends thereof respectively lying in helical grooves formed in the rod sections 108. The coil springs 136 are under tension and the extremities thereof may be tack welded in place to provide the necessary tie between the parts 122 and 128 of the tie rod assembly.

The boom assembly 42 includes, in addition to the boom tube 44, an elongated housing 138 for the boom tube. The boom tube 44 is movable relative to the housing in the direction of its longitudinal axis to feed the abrasive wheel 78 back and forth across the work piece

2,845,751

W. Suitably secured within the housing 138 adjacent the inner end thereof is a sleeve 140. having a bearing 142 secured within, the sleevj 140 (see Figure. 7). The outer end of the bearing 142. abuts an internal shoulder on the sleeve and is clamped there against by an annular disc 144. The bearing 142 supports the inner end portion of the boom tube both for axial sliding movement and for rotation.

Referring now to Figure 5, the outer end portion of the housing 138 has secured.therein, a sleeve 146 and secured within the sleeve is a- bearing 148. The inner end of the bearing 148 abuts an internal shoulder on sleeve 146 and a plate 150 is secured to the outer end of sleeve 146 by bolts 152, thereby confining and clamping the bearing 148 against axial shifting movement. The bearing 148 supports the outer end, portion of the boom both for axial sliding movement and for rotation.

The. boom tube 44 is reciprocated in the direction of its longitudinal axis relative to the housing. 138 by a motor in the form of a double acting hydraulic piston cylinder assembly 154. Opposite ends of the cylinder 156 of the assembly 154 are secured to the under side of the housing 138 at longitudinally spaced points and a piston rod 158 secured to the piston of the assembly 154 extends beyond, the inner end of the assembly and is pivotally connected to a clamp 160 by means of a transversely extending pin 162 (see Figure 7). The clamp comprises upper and lower clamping parts 164 and 166 which cooperate to encircle the reduced inner end portion 165 of boom tube 44 in a manner permitting rotation of the boom relative to the clamp. It will be apparent that inward and outward reciprocation of the, piston of the hydraulic assembly 154 will result in a corresponding movement of the boom tube 44 relative to housing 138.

The assembly 154 is operated in a, manner more fully described hereinafter. Briefly, as shown in Figure 15, the assembly is connected to fluid pressure supplied by a duplex pump assembly 37 and is selectively operated by a suitable four-way three position valve 170 mounted on the carriage frame structure. Valve 170 is controlled by a control element 171.

The boom assembly 42 is mounted upon the carriage 12 for swinging in a vertical plane in order to move the abrasive wheel into and out of engagement with the work piece W. Referring now particularly to Figure 6, it will be noted that the housing 138 has secured therewithin a block 172 which is provided with a central through passage for loosely accommodating the boom tube 44. Projecting laterally from opposite sides of the block 172 through openings in the side of housing 138 are trunnions 174 and the latter are respectively journalled in roller bearings 176 supported by the base of the U-shaped part 178 and the bracket 180 respectively. The U-shaped part 178 and the bracket 180 are secured to a part 182 of the carriage structure by bolts 184. The arrangement is such as to permit vertical swinging movement of the boom assembly 42.

Referring now to Figures 4 and 5, it will be noted that four pairs of rollers 186 are respectively journalled on the plate 150 at opposite sides thereof in positions to engage laterally spaced vertically extending guide members 188. The guide members 188 are portions of a frame 189 secured to a part 190 mounted on the carriage 12. It follows from the foregoing that the boom assembly 42 is accurately guided throughout its vertical swinging movement about the pivot axes of trunnions 174.

A counterbalancing weight 192 is provided for the boom assembly 42 which is movable along the axis of the boom in opposed relation to the in and out sliding movement of the boom. The counterweight 192 operates to reduce the pressure of the grinding wheel on the work. Referring to Figures 3 and 12, it will be noted that a housing extension 194 is provided at the inner end of β

the boom housing 138. The counterweight 192 is feciprocable within the housing extension 194 in the direction of the boom tube axis. Suitably secured within the upper portion of the housing extension 194 are a pair of 5 channel-shaped rails 196 which are disposed in laterally spaced relation and which open laterally outwardly. These rails 196 extend parallel to the axis of the boom tube 44. A pair of hangers 198 respectively have their lower ends secured to the counterweight 192 and have rollers 200 10 at their upper ends positioned to have rolling engagement with the lower flanges 202 of the rails 196, enabling the reciprocation of the counterweight in the direction of the boom tube axis.

Fixedly secured to the base of each channel-shaped 15 rail 196 at points adjacent opposite ends thereof are the depending brackets 204. The brackets 204 adjacent the outer end of the housing extension 194 are arranged in laterally opposed relation and respectively rotatably support the opposite ends of a shaft 206 to which is secured ²⁰ a centrally disposed sprocket 208. The brackets 204 at the inner end of housing extension 194 also are arranged in laterally opposed relationship and rotatably support the opposite ends of a shaft 206 also having a centrally disposed sprocket 208 secured thereto. A chain 210 extends ²⁵ around the sprockets 208. Referring to Figure 7, it will be noted that the clamp 160 has a depending projection 212 which is secured to the upper run of chain 210.

Referring again to Figures 3 and 12, it will be noted that each shaft 206 has secured thereon a pair of sprockets ³⁰ 214 at opposite sides of the intermediate sprocket 208. Chain 216 extends around the sprockets 214 of each shaft at one side of sprocket 208 and chain 218 extends around the sprockets 214 at the other side of the shaft. The counterweight 192 is formed with the upwardly extending ^3o projections 220 which are respectively secured to the chains 216 and 218. As a result of this construction, the counterweight 192 will be moved in directions opposite to the direction of movement of the boom tube 44 so that the grinding pressure of the wheel on the work piece ⁴³ is reduced. However, as pointed out above, while it is necessary to obtain a uniform grinding pressure of the wheel upon the work as the boom moves along its axis, it is not feasible to accurately counterbalance the boom to obtain this result by weights alone. This will be 45 appreciated when it is considered that a number of other assemblies move with respect to the boom pivot axis during axial sliding of the boom, such as the hydraulic motors and the electric motor for the abrasive wheel. In order to accurately counterbalance the boom, a hold 50 down mechanism is employed which will be described below.

As pointed out above, the boom tube housing 138, together with the boom tube 44 may be swung vertically about the axis of trunnions 174, This is accomplished 55 by a motor in the form of a double acting hydraulic piston cylinder assembly 222, the cylinder 224 of which is pivoted to the carriage 12 for rotation about the axis of pivot pin 226 (see Fig. 8). The assembly 222 is disposed generally vertically beneath the boom assembly put60 wardly of the pivotal mounting for the boom assembly and the piston of the fluid motor has a piston rod 228 projecting from the piston of the assembly 222 which extends upwardly through the top of cylinder 224 and is pivoted to the bottom of plate 150 by a pin 230.

As will be more fully described hereinafter, the piston of assembly 222 is moved in opposite directions in cylinder 224 by fluid under pressure supplied by the duplex pump assembly 37. The flow of fluid under pressure to cylinder 224 is controlled by a manually operated four 70 way two position valve 232 mounted on the carriage and controlled by a control element 233.

It is often desirable to tilt or oscillate the boom in opposite directions about its axis. One purpose of this is to maintain the wheel in properly dressed condition. 75 This may be accomplished by rotation of the boom 44

2.845.751 in the bearings 142 and 148. As seen in Figure 7, a sleeve 234 having an internal bore of uniform non-circular (in this instance square) cross section is secured in the inner end of boom tube 44. Extending into the noncircular bore of sleeve 234 is a rod 236 of like non-circu- 5 lar cross section throughout its length. The rod has its reduced and threaded inner end projecting freely through channel bracket 238 fixed to housing extension 194. Washer 240 is interposed between the shoulder 241 on rod 236 and plate 242 secured to bracket 238, and washer 10 244 is interposed between nuts 246 threaded on the end of rod 236 and plate 248 secured to the bracket. As a result, the rod is supported by the bracket in a manner preventing axial sliding but permitting rotation of the rod. 15

The rod 236 is slidable in the bore of sleeve 234, and is rotated by an arm 250 secured to the rod and projecting upwardly therefrom through an opening 252 in the top of housing extension 194. Rotation of arm 250 correspondingly rotates the rod. ²³

As shown in Figures 13 and 14 the radially outer end of arm 250 is formed with a radially extending slot 254 and a roller 256 is slidably supported in the slot. The roller is mounted on a driving member 258 which in turn is secured to the power output shaft of a speed ²³reducer 260. The speed reducer is connected by a pulley 262 and belt 264 to an electric motor 266. The motor 266 and speed reducer 260 are secured to the top of housing extension 194. Roller 256 is eccentrically located with respect to the axis of rotation of driving member ³³258 so that the arm 250 is rocked in opposite directions in response to rotation of the driving member. The boom may thus be oscillated by rod 236 irrespective of the axial position of the boom with respect to the rod.

The electric motor 266 may be suitably connected in ³³an electric circuit for convenient control by an operator on the carriage. A suitable wiring circuit and control therefor are shown in the application of Anthony A. Muehling Serial No. 345,484 filed March 30, 1953.

Referring to the diagram in Figure 15 it will be noted ⁴³that the duplex pump assembly 37 comprises three pumps 270, 271 and 272 driven by an electric motor (not shown). The pumps 270 and 271 are of the rotary blade type and the intake sides thereof are connected by a conduit 274 to a reservoir 275. The reservoir contains a 45 supply of hydraulic fluid and is suitably supported on the carriage.

The delivery side of pump 270 is connected through a relief valve 276 to the intake port 2A of valve 39. The intake port 2A in position 1 of valve 39 is con- 50 nected to port 5A of the valve which is connected to the reservoir 275 by a conduit indicated by the broken line 277. The ports 3A and 4A of valve 39 are closed in position 1 so that fluid under pressure from pump 270 is bypassed back to the reservoir. In position 2 55 of valve 39, fluid is delivered to the motor from port 4A through conduit 278 and flows from the motor back to the reservoir through conduit 279 and port 3A. In position 3, the motor is driven in the reverse direction from that of position 2. 60

The intake side of gear pump 272 is connected to the reservoir by a conduit 280 and the delivery side of the pump is connected through a relief valve 281 to the intake port 2C of valve 170. In position 1 of valve 170, the intake port 2C is connected by port 5C to the return 65 line 277 to the reservoir. The ports 3C and 4C are closed in position 1 so that fluid under pressure from the pump 272 is returned to the reservoir. It will be apparent that in position 2 of valve 170 the boom will be moved inwardly along its axis because the intake 70 port 2C is connected to port 4C which is connected to the head end of assembly 154 by conduit 282 and fluid at the rod end is exhausted through conduit 283 to the port 3C communicating with exhaust port 5C.

The intake side of the pump 271 is connected to the 75 ⁸ reservoir by the conduit 274 and the delivery side of the pump is connected through a relief valve 284 to the intake port 2B of valve 232. In position 1 of valve 232, port 2B is connected to port 3B and the latter is connected to the piston cylinder assembly 222 above the piston thereof by a conduit 285, a pressure regulating valve 286 which will be more fully described hereinafter, and a conduit 287. It will also be noted in position 1 of valve 232 the assembly 222 below the piston is connected to port 4B of the valve by a conduit 288, the port 4B communicating with the port 5B which returns the fluid to the reservoir through the return line 277. Thus in the Figure 1 position of valve 232, the boom 44 will be lowered.

The boom will be raised in the No. 2 position of valve 232 as is readily apparent.

The pressure regulating valve 286 is shown in Figures 2, 15 and 16. This valve is provided to determine and regulate the pressure of fluid delivered to the pistoncylinder assembly 222 in position 1 of valve 232 urging the boom in a downward direction. Referring particularly to Figure 16, it will be seen that valve 286 comprises a casing 290 and the conduits 285 and 287 extend into the casing and communicate with each other at their junction with the longitudinally extending bore 291. The bore 291 extends entirely through casing 290 and has a needle valve element 292 therein. The valve element 292 has one end tapered to a point and adapted to seat in the frusto-conical opening 293 of plate 294 clamped against the end of casing 290 by a hollow cap 295. The return conduit 277 communicates with the hollow interior of cap 295.

It will be seen that bore 291 has an enlarged threaded portion 296 and that valve element 292 has a portion threadedly engaged therewith, whereby rotation of the valve element relative to the casing will shift the valve element toward and away from the valve seat to vary the size of opening 293. It will be apparent that if the valve element completely closes opening 293, the full pump pressure will be delivered to the assembly 222 to apply a maximum downward pull upon the boom. The pressure of the fluid delivered to assembly 222 to lower the boom will progressively diminish as the valve element is backed away from the seat, that is shifted to the left as viewed in Figure 16, since more and more fluid is thereby bypassed to the return conduit 277.

Since the effect of gravity causes the abrasive wheel to be urged downwardly against the work with a greater force in the “out” position of the boom, it is necessary to gradually reduce the pressure of the fluid delivered to assemby 222 to urge the boom downwardly as the boom moves “out,” or to the left in Figure 1, to account for the increasing effect of gravity.

As pointed out above, one of the principal reasons for employing assembly 222 as a hold down device for the boom is the fact that it is not feasible to completely and accurately counterbalance the boom by weights alone throughout its in and out movement so that the pressure of the wheel upon the work is uniform in all positions of axial movement of the boom. This is due in part, at least, to the fact that, in addition to the boom, a number of other parts, such as the various hydraulic and electric motors, move relative to the boom pivot axis which are practically impossible to accurately counter-balance. In the present instance, while the counterweight measurably reduces the weight of the abrasive wheel upon the work, still the wheel may bear against the work with 100 pounds more force in the extreme “out” position than in the extreme “in” position, due to gravity. In this instance, it is desirable to have the pull down device 222 add to the force of the wheel against the work by an amount which is 100 pounds greater in the “in” position than in the “out” position and which progressively varies between these positions.

Referring now to Figure 2, it will be noted that car

2.845.751 ⁹ riage 88, which supports the abrasive wheel motor and is, of course, movable in accordance with the axial movement of the boom, has a bracket 300 depending therefrom and secured to the upper reach of a cable 301. Cable 301 is trained over pulleys 302 mounted on the frame structure of carriage 12 and the cable also is trained over pulley 303 on gear box 304 supported on carriage 12. The output shaft 305 of the gear box has an annular disc 306 sleeved thereon, the disc having a hub portion axially adjustably secured to shaft 305 by a set screw 307. A circular disc 308 is secured to the outer end of valve element 292 which has a plurality of circumferentially spaced openings arranged in diametrically opposed relation in a circular array adjacent its periphery. As seen in Figure 16, a pair of pins 309 project from disc 306 and enter diametrically opposed openings in disc 308 so that the valve element 292 is rotatable as a unit with shaft 305 of the gear box.

It will be apparent that as the boom moves along its axis between extreme “in” and “out” positions, that the valve element 292 will move toward or away from the seat to vary the pressure of fluid delivered to the upper end of the assembly 222. In the present instance, the valve element moves axially in a direction toward the valve seat, to increase the pressure of fluid delivered to the upper end of assembly 222, when the boom moves inwardly—or to the left in Figure 2, and the valve element moves away from the seat, to decrease the pressure of fluid delivered to the upper end of assembly 222, when the boom moves outwardly. There will be a gradual substantially “straight-line” variation in the pressure delivered to the assembly 222 by valve 286 as the boom moves axially.

Not only does the hold down assembly 222 make it possible to completely and accurately counterbalance the boom so the abrasive wheel bears upon the work with a constant pressure irrespective of the axial position of the boom, but chattering of the wheel on the work is eliminated. As pointed out above, even where the boom is counterbalanced to be tool heavy, there is a tendency to chatter where no positive resistance to upward swinging of the outer end of the boom is provided. It is apparent that in addition to the actual pull down pressure applied by assembly 222, the hydraulic fluid therein provides a positive resistance preventing upward swinging of the boom to eliminate chattering. This positive pressure resistance to upward swinging is much greater than the actual pull down pressure and is determined by the setting of the pressure-regulating valve 286. The valve 286 bypasses hydraulic fluid back to the reservoir at a rate determined by the size of the opening or metering orifice to maintain a predetermined downward pressure on the boom. It will be understood that if, for any reason, forces are encountered tending to raise the boom, as where irregularities in the work piece are encountered, or in instances where the boom begins to chatter in a vertical plane, the body of hydraulic fluid in the hydraulic piston cylinder assembly 222 will positively resist any such upward movement. The magnitude of the forces set up by the body of hydraulic fluid will, of course, depend upon the size of the metering orifice 293 since this orifice provides an escape for the body of hydraulic fluid in the assembly 222. However, due to its small size, the rate to which it will release fluid from the assembly 222 is likewise small and, accordingly, the pressures resisting upward movement of the boom are great. As pointed out, the actual resistance to upward swinging is determined by the setting of the pressure-regulating valve 286. The valve 286 may be very simply adjusted by mere loosening of set screw 3C7 and retracting disc 306 to withdraw pins 309 from the openings in disc 308. Then the boom may be moved inwardly or outwardly a predetermined distance and the disc 306 advanced to engage pins 309 in the aligned pair of openings in disc 308.

The operation of the machine will be readily apparent from the foregoing. The carriage 12 may be moved in opposite directions along track 10 by selective motion of valve 39 to position 2 or position 3. The boom may be oscillated or rocked about its longitudinal axis by the 5 electric motor 266 having suitable controls available to the operator. The boom may be moved in and out along its axis by selective shifting of valve 170 to position 2 or 3. Finally the outer end of the boom may be raised or lowered by operation of valve 232. In posi10 tion 1 of valve 232, the boom is urged downwardly with a variable pressure determined by the perssure regulating valve 286. In position 2 of valve 232, the outer end of the boom is raised to move the abrasive wheel away from the work.