US2267391A - Abrading machine - Google Patents

Description

C. J. ASTROWSKI ABRADING MACHINE Filed Aug. 3, 1940 bil.

' by JS/WfMM/f HIS Attorn ey.

t Patented 1941 .I

charles .1. asti-omai, Schenectady, N. y., assigner to General Electric Company, a corporation of New York appueadonnugcst s, 1940, serial No.' :sans

(ci. s1'1cs) lclaims.

My invention relates to abrading machines and particularly to automatic precision abrading machines for nishing'work pieces uniformly within extremely closetolerances. y

Automatic abrading or grinding machines are commonly provided with gauging or calipering devices arranged to actuate a mechanism vfor terminating the grinding operation when the work has been reduced to a predetermined size. It has been found extremely difilcult to construct an automatic grinding machine in which work pieces may be .iinished `uniformly within close tolerances. This diillculty is due in part to the effect of the momentum of the moving parts of the machine and the inability of the control deviceto compensate for the continued movement of .the

grinding wheel and carriage after initiation of the stopping operation. Further difiiculties arise l because of lost motion inthe machine and the iiexibilityof'certain parts of the control mechanism. Extremely high accuracy of the gauging or calipering device used to determine the size of the 'work becomes ineffective if the automatic control is unable to stop the grindinggoperation witlin the desired limits fof size of the finished wor AIt is an object of my invention lto provide an improved abrading machine including a mechanism for eifecting an extremely low rateof relative movement between the abrading tool -and 30 the work.

Another object of my invention is to provide automatic abrading machine including an improved device for 'controlling the abradin'g operation to finish work pieces uniformly within ex- .tremely close limits of accuracy.

Y Another object of my invention is ilo-provide an automatic abrading machine having an im provediiuid operated driving mechanism which shall make possible the iinishing of work pieces" within extremely :man miennes.

Anutnerobjeaormymvenuoniswpm'vide an improved automatic abrading ineluding a control device arranged to minimize any enect of thecontinued operation of the abrading ing in which Fig.`1 is a diagrammatic side elevation view of an external grinding machine em- `my invention, the conventional work holder including a head-stock and driving mechanism being omitted to avoid complication of the drawing; and Fig. 2 is a front view of a portion of the machine ofl Fig. 1 showing the work in position in the work holder. v

The grinding machine illustrated in the drawing is a type in general use and comprises a base on which are mounted a work holder and a driving mechanism -for rotating the work and a transverse wheel slide on which are mounted a grinding wheel and a motor for driving the wheel. Suitable power mechanism is provided for rotating the work and for moving the wheel toward and away from the work to Veilect the grinding operation. In the machine'illustrated, the .wheel slide is actuated by hydraulic operators or fluid motors. The forward operation of the grinding wheel toward the work is started manually. A suitable work measuring or calipering gauge is maintained in position on the workl during grinding and is provided with contacts in an electrical circuit for controlling the operation ol' the fluid motors. The control is suchthat after the work has Abeen reduced to a rst predetermined size. the gauging mechanism operates to reduce'the rate of feed of the wheel toward the work for a iinishing cut. After the work has been finished operation is at such a low rate that the forward movementof the wheel and carriage can be terminated and-the'carriase reversed before the continuedv rotation of the wheel can:

reduce the work beyond the predetermined limits of tolerance. An extremely low rate of feeding of the wheel vslide is obtained by providing a stop to limit the forward movement of the slide which can be produced by operation otite-driving motor. Movement of the stop is controlled by a tool and drivingmechanism afterthe initiation of me stopping of the abrading'onerauon. Y

Further .objects and advantages of my invention will become apparent 'as thefoliowing de-. scription proceeds and the features of novelty which characterize my invention will be pointed out with particularityi'fthe 'claims annexed to andformingapartofthisspeeiiicatlon.

For a better understanding of Vmy invention. reference maypehadtotheaccompany'ingdrawcam which is designed so thatit may be moved through a. wide range while allowing only avery small movement of the stop. The cam preferably is driven by a mnd-motor supplied by fluidunderprsurefromthesamesourcethatmpliesthemotorfordrivingthewheel slide. The` control vof the rate of movement ofthe cam can then be effected by a suitable valve for changing rate of flow of fluid for actuating the cam j drivingmotor. 'QF Referring now to the drawing, .the abrading machine shown in Fig. 1 comprises a base Il on which is mounted a wheel carriage or slide Il which is arranged to slide transversely of the base 'I9 on a plurality of guides I2 of V-shaped cross-section in a manner well known in the art. On the wheel carriage II are mounted a grinding wheel I3 and a. motor I4 connected to drive the wheel through a belt I4. The work piece to be ground is mounted in a suitable work holder for rotationon a longitudinal axis which is normally parallel to the axis of the wheel I3. I'he work piece is indicated at I5 in Fig. 1, and in Fig. 2 I have shown the work mounted in a work holder comprising a head-stock |1 and a suitable chuck I8 for gripping the work. The head-stock I1 may be arranged to slide longitudinally o'f the base III on an axis at right angles to the guides I2. As shown in Fig. 2, the grinding wheel I3 may be removed by loosening a suitable nut I5 and removing the nut and a collar I 5'.

The arrangement illustrated in which the wheel is moved toward the work is one commonly employed. However, itis obvious that any suitable arrangement for moving the wheel and the work holder relatively to one another so that the wheel can be moved toward and away from the work might be employed; for example, in some cases it might be found desirable to hold the wheel stationary and to move the work. 0bviously the same power and control devices may be employed for either arrangement.

In order to finish the work within close tolerances, it is desirable that the abrading machine be arranged to feed the wheel toward the work at a very low rate of speed, and I prefer to employ a iiuid pressure or hydraulicmotor as'the power device in order to obtain smooth operation and accurate and exible control. In the arrangement shown in the drawing, a'tiuid motor |9 comprising a cylinder 25 and a piston 2| is arranged to drive a power transmitting vshaft 22` which is connected to the wheel slide through a suitable lug or driving connection 23. Power for driving the motor |9.is providedby a fluid pressure pump 24 arranged to pump oil or.

other suitable liquid from a tank 25 through a connection 25 and a control or reversing valve 21 either to.a forward feedline 25 or to a return feed line 29, the fluid returned from the motor I9 llowing back to the tank 25 through one or aaeaaai pump 24 is maintained in direct communication with the forward feed line 25 through a suitable slot and the return feed line 29 is in direct communication with the connection 30 through a slot 4|. The slots 40 and 4| are in the form of annular grooves around the slide 3|. When the slide is in its right-hand position, uid is forced by the pump 24 to the left-hand side of the piston 2| through the forward line 28 and drives the motor I9 to move the wheel slide toward the work; fluid forced out of the right-hand side of the piston 2| is returned to the tank 25 through the line 29, the slot 4I, and the connection 39.

In order to determine the size of the work .piece'as it is being ground. I provide a. suitable gauge orv calipering device 42. The gauge 42 is pivotally mounted at 43 on an arm 44, the arm 44 being pivoted at 45 to a stationary member 49, and a handle 42a is provided for moving the gauge about its pivot 45. This pivotal mounting of the gauge is provided in order that the gauge may be moved out of its position adjacent the Work so that it will not be in the way when the workpieces are being placed in or removed from the work holder. The retracted position of the gauge is indicated by ydotted lines, the arm 44 having been pivoted upwardly in a counter-clockwisel direction. A suitable spring 41 mounted in a stop 48 provides a buffer to prevent shock when the arm 44 is lifted; anda spiral spring 49 is arranged to hold thegauge in its raised position. The gauge comprises a head 50 on which ls mounted an arm 5| having two contacts 52 and 53 for positioning the gauge against the work and a sliding contact or feeler 54 arranged to slidein the head 50 and indicate the size of the work. An indicating dial or gauge 55 may be connected on the head 50 and engaging the feeler 54 through a rod 56 to indicate the diamthe other of the lines 2l and 29, the valve 21 and a connection 30. The valve 21 is provided with a slide 3| arranged to be actuated by a manually operable handle 32 connected to the slide through a lost motion link 33 and a rod 34. the rod 34 having a pin 35 fitting in a slot 35 in the link 33. The slide 3| has been shown in its position for driving the motor I9 to move the wheel away from the work. When the valve is in the po'sition shown, the fluid from the pump 24 iiows through a diagonal cross duct 31 in the slide and thence through the return feed line 29 to the right-hand side of the piston 2 I, thereby. forcing the piston to the right.' Any oil or uid on the left-hand side of the piston is forced out through the forward feed line 23 to the. valve 21 and thence through a diagonal cross duct 33 i to the connection 35 and back to the tank 25.

When itis desired to operate the motor I9 to move the slide toward the work. the handle 32 is moved to the right and pulls the slide 21 to its right-hand position. Upouvits release the handle 32 is returned to the position shown by a suitable spring 39. When the slide 3| is in its right-hand position, the connection 25 from the eter of the work. Thezgauge 42 is arranged to actuate electrical contacts in a circuit for controlling the operation of the abrading machine A 'to terminate the grinding operation whenever the work has been finished to a predetermined size. Whenever the work has been nished to a predetermined size, a circuit is energized to actuate a `solenoid 51 having an armature or plunger 59 connected tothe slide 3| of the valve 21. Energization of the solenoid 51 pulls the slide 3| to its left-hand position and thereby reverses the motor I9 and withdraws the wheel slide Il to separate the wheel and the work. In order that the control arrangement shall besensitive to. slight variations in the size of the work, I provide -a high ratio leverage system for actuat ing the control contacts by means of the feeler This lever system comprises an arm 59 plvoted to the gauge. head at 59 and arranged to engage a second arm 5| at 52, the arm 6| being pivotally mounted on the frame of the gauge at 53. It will be obvious that with the arrangement of the pivoted arms 59 and 6| a very slight movement of the feeler 54, which engages the arm 59 at 64, will effect a considerable movement of the end oi' the arm 5|. An electrical contact 95 is mounted on the end of the arm 6I and is arranged to engage an adjustable stationary contact to close the circuit of the solenoid 51. Power for energizing the circuit ls received from an alternating current source 61 across which iscounected the primary winding of a transformer 55. Oneside of the secondary of the transformer 59 is grounded and the other .side is connected to the solenoid 51 through a switch 99. 'I'he switch 59 is biased to its closed.

g the movable contact 65 and the arm 6| to the frame ofthe gauge which is grounded by a connection 12. The switch 1| may be used to cut out the automatic stopping of the machine when manual operation is desired. From the foregoing, it will be seen that when the work has been ground to a predetermined size, the contact 69 will engage thefxed contact 66 and complete the electrical circuit for energizing the solenoid 51 therebypullngthe valve slide 2i to its lefthand position and withdrawing the wheel slide to terminate the grinding operation. The posi tion of the point of engagement between the contacts 65 and 66 may be selected byoperation .of a thumb screw 12 which raises and lowers the contact 66. The adjustment of the thumb screw 12 determines the size to which the work is finished when the grinding operation is termi'- nated.

With the machine in the position shown in Fig. l, the grinding operation is started by pushing the handle 32 to the right to operate the motor I9 and move the wheel toward the work; the force transmittingrod 22 moves to the right and a dash pot15 secured to the end of the rod moves to the right with the rod until a plunger 16 of the dash pot engages a stop 11 mounted on an arm 18 pivoted on base I9 at.1'4. When the plunger 16 has engaged the stop, the rate of forward movement of the wheel toward the work is decreased by iluid vpressure against the plunger 16. When the dash pot 15 is forced to the right with respect to the plunger 16 oil within a chamber19 is1 forced out through a conduit 66 against the pressure of the pump 24, the outlet of the ,pump being connected directly with the chamber 19 through a restricted opening 8l. The sizeof the opening 6I may be adjusted by a thumb screw 82. Whenever suiilcientfiuid has been forced out of the chamber 19 to permit engagement ofthe inner end of the plunger 16 with the closed end of thedash pot 16, furthermovement of the rod 22 to the right lis prevented, the

movement of the motor I9 then being restricted bythe stop 11. I have found that by providing an auxiliary device. for controlling movement of the stop 11 to modify the operation of the motor I9, very accurate control of the movement of the wheel toward the work can be eilfected;l furthermore, by providing a suitable devicel such as a cam, it is possible to control the machine so accurately that the elfects of the momentum of the carriage II and of the wheel I2 cannot reduce the work below a predetermined limit of size after the initiation of thestopping operation. In' the arrangement illustrated, I have provided an' elongated wedge-shaped cam 92 slidably I' mounted for longitudinal movement'in a fixture forced out of the chamber 19 ofthe dash pot 16 upon operation of the motor i9, further` rnov'e-4 ment of the motor I9 will be dependent solely =uponmovement of the cam 62. By'suitabie conwhich affords movement of the stop 11 by allowing the .follower 95 to roll down the slide 92a of the cam, it is possible to effect a very low rate of movement of the wheel toward the Work. In order to obtain very accurate control of the movement ofthe cam 62 and to obtain variable speed of the cam, I prefer to employ a hydraulic motor 86 having a piston 81 connected to drive the' cam 62 through a rod 69. The motor 86 is provided with fluid under pressure from the pump 24 under control of the valve 21. The motors I9 and 86 are. therefore, operated simultaneously.. When the machine is started lby moving the slide 2i of the valve 214to the right, llid 11D- 11 and the cam is not completely effective to con- .trol the movement of the carriage until the fluid has been forced from the chamber 19 of the dash pot. .By designing the cam surface 63a so that the cam can be moved longitudinally through a relatively great distance to effect a very small movement of the cam follower 95, it is possible to attain a very high degree of accuracy in the grinding operation since a very low rate of movement of the wheel carriage may be attained and I since the rate of movement is very uniform. A

further reduction in the movement of the. carriage Il for a given movement of the cam follower 85 is obtained by the leverage of the arm 16. It will be-noted that the cam follower 65 is at the end of the long arm of the lever, while the stop' 11 is on the 'short arm of' the lever, the

`movement of the stop 11 being less than the movement of the cam follower in accordance with the ratio of the short arm of the level to the long arm-thereof. The valve 96 is arranged to control the rate of discharge of uid from the cam driving motor86 and therefore controls the rate of iiow of the uid into the motor which determines the motor speed. I provide the valve 99 inorder to obtain a high degree of accuracy of the control of the cam and also .to provide two speeds of operation, one speed for the initial cut or rough grinding operation, and a lower speed for the finishing operation. The valve 99 com prises a slide' 92 mounted in a valve body 9| having uppervand lower chambers and 96, respectively, separatedV by a suitable partition, the chamber 95 being in communication with the upper chamber of the motor 86 through the connection 89, 'and the chamber 96 being in comf- .munication with the tank95 through the drain conduit 9i. ,The slide 92 is provided with a tapared slot 91 which provides a variable opening betweenV the chambers 95 and 96, the size of the opening depending upon the position of the slide 92 inthe valve body 99. In the bottom position of the slide 92 as illustrated, the opening between the chambers 95 and 96 is' restricted, and when the slide is raised to its upper position the open-'- ing is relatively free. The slide is arranged to be to its upper position by a solenoid 98 vhaving an amature 99 for raising the slide 92 in opposition towa spring |99, The lower position of -the slide -92 which controls the lower speedfor trol of upward movement of the` caxn 499, .75 une feed may-be adjustedby a thumb screw' 19|.

and the upper position of a slide which determines the higher speed for coarse feed may be adjusted by a thumb screw |02.

The position of the valve 90 to provide the coarse and ilne feeds is controlled by the gauge mechanism I2 which is provided with a set of contacts for controlling the circuit of the solenoid 98. During the operation of the machine, as

soon as themotor I9 has moved the dash -pot 15 to the right, the switch 89A is closed by its biasing spring 69a which iseffective as soon as the dash pot 15 releases the arm 89h.- The closing of the switch 69 energizes the solenoid 88 by connecting it to the secondary of the transformer 61 and through a manual switch |05 and a spring contact arm |05 on the gauge with the return circuit or ground through the arm Si. 'I'he spring arm |06 has a contact |01 which is maintained in engagement with a contact 08 on the arm 6| as long as the work piece is above a predetermined size and the valve 90 is therefore actuated by the solenoid 98 to maintain the slide 93 in its upper position thereby ad-f vancing the cam 83 at its higher rate of speed to operate the wheel I3 and reduce the work at a relatively high rate. Whenever the work has been reduced to the above-mentioned predetermined size, the downward movement of the arm 5I causes a separation of the contacts vS01 and |08, the point of separation depending upon the adjustment of a thumb screw |09 the upper ating position, the handle 32 when released movend of which provides a stop limiting movement of the arm |08. The opening of the contacts |01 and |08 deenergizes the solenoid 98 and causes the valve slide 93 to move to its lower position thereby restricting the flow of fluid from the motor 86 which then moves the cam at a greatly reduced rate of speed. 'I'he wheel slide f I-I then advances very slowly to make the finishing cut until the work is reduced to a predetermined size within the permissible limits of tolerance and contact 55 engages thecontact 80;

this energizes the solenoid 51 to move the valve slide 3| to the left and reverse the cam and wheel slide motors thereby terminating the" grinding operation.. Fluid from the pump 2| for reversing the motor 06 is supplied from the return feed line 29 through a check valve IIII, the valve 90 restricting the flow throughconnection 89 so that the iiuid pressure is effective to lower the piston 81. The switch |05 may be used to cut out the contactsV |01 and |00 by grounding the switch on a connection when the fine feed control is not required or when it is to be i controlled manually.

I have found that by a suitable design of the surface 83a of the cam 83, it is possible to operate a grinding machine to finish work pieces uniformly within an extremely high degree of accuracy. For example, one hydraulically powered machine which was tested was provided with a gauging mechanism of the type illustrated on the drawing having `a leverage ratio of 180 to 1 between the contact 85 and the feeler 54. The Y machine was further provided with a lever corresponding to the lever 18 having a ratio of 3 to l Y between the cam follower 85 and the stop 11. The surface of the cam' 83 was provided with a slope of .008 inch per inch of length. Work pieces finished on this'ma'chine and tested by means of an electrical gauge were found to have J been finished uniformly within one half of one ten-thousandth-(.00005) of an inch.

During the operation of the abrading machine illustrated,'-the machine is initially in the posi- `ing back to its position as shown by the action of spring 39. The pump 20 then supplies uid under pressure to produce forward motion of the motors I9 and 88, the piston` 2| moving to the right and driving the wheel slide forward until the plunger 'i6 of the dash pot 15 engagesv afford relatively free flow of fluid through the valve so that the motor 85 may be actuated at its higher speed. The cam 83 moves upwardly and the stop 11 is moved to the right at the higher rate dependent upon the high speed movement of the cam 83. The grinding wheel moves forward into the work and as soon as the work has been reduced to a predetermined size, which is the limiting size for the rough cut, the contacts |01 and |08 separate and break the circuit of tne solenoid sa; thereupon the slide 93 moves to its' bottom position and restricts the ow ofl uid through the valve 90 thereby reducing the speed of the motor 88 to its low speed and moving the cam and carriage at minimum speed for the nish grinding cut. As soon as the work has been reduced to a second predetermined size which is within the permissible limits of accuracy, the contact 85 engages the contact 50 and thereby energizes the solenoid 51; this moves the slide 3| of the valve 21 to its left-hand position to reverse the motors` and withdraw the wheel from the work and return the 83 to its' position as shown in the drawing. When the work has been nished, the gauge I2 is removed from the work and placed in its raised position manually by means of handle 02a. y

By designing the slope 83a of the cam 83 so that the cam is movable through a relatively wide range to afford a small range of movement of the cam follower 95 by operation of the motor iii, it is possible to insure separation of the grinding' wheel and the work before the momentum of the slide and the continued operation ofthe wheel, can reduce the work below the predetermined permissible minimum limit ofl size. 'This feature of the operation which minimizes overgrinding due to the momentum of the wheel and its slide also minimizes inaccuracies due to irregularities or lost motion in any of the moving parts of the machine or its control and, thereby, makes possible the flnishing of work pieces in large numbers with great uniformity and within very close limits of accuracy.

It will readily be apparent from the foregoing that I have provided a simple and .eiiective arrangement for insuring laccurate and uniform finishing of work pieces within very small limits or tolerances; and further that the high degree of accuracy is effected with a' device of simple aacasei and rugged construction. Although I have shown a particular embodiment of my invention in cone nection with an external grinding machine, other applications will readily be apparent to those skilled in the art. I do not, therefore, desire my invention tobe limited to the particular construction shown and described, and I intend in the appended claims to cover all modifications within'the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An abrading machine comprising a work holder and an abrading tool which are relatively p to one another into and out of a Working range,

movable to feed the `tool toward and away from the work, power means for effecting such relative movement. means including a cam and arranged to provide a stop for said power means for determining the rate of movement of said tool toward the work, and means dependent upon the reduction of the work to a predetermined size for stopping the operation ofl said power means to move said tool toward the work, said cam being movable through a Wide range to aiord a small movement of said tool toward the work whereby any further reduction of the work caused by operation of saidtool after initiation of the stopping of said power means will lie within a predetermined permissible working tolerance.

2. An abrading machine comprising a work holder and an abrading tool which are relatively movable to feed the tool toward and away from the work, power means for effecting such relative movement, means including a cam and arranged to provide a stop for determining the rate of movementof said tool'toward 'the work, means dependent upon a reduction of the work to a rst predetermined size for reducing the rate of movement of said cam,V and means dependent upon `the further reductionof the work to a second predetermined size for stopping the operation of s aid power means tozmove said tool toward the work, 'said cam being movable through a wide range to afford a small movement of said tool toward' the work whereby any reduction of the work below said second predetermined size caused by operation of said tool after initiation of the `stopping of said power means will lie within a predetermined permissible working tolerance.

3. An abrading machine including a work holder and an abrading tool, power means for moving said work holderand said tool with respect to one another into and out of a working range,

a', movablestop arranged to cooperatewith said power means to4v restrict 'the movement [of `said tool and said holder toward said working range, vmeans including a cam 'arranged to aiiord movement of said stop by said power means for determining the rate of lmovement or said tool and said work holder with respect to one another within said working range, and means dependent'A .upon the reduction .ot lthe work to a predetermined size for actuating said power means tov move said tool and said holder apart with respect y to one another and out of said working range.

, 4. A'n abrading machine including a work holder and an abrading tool, power means including a member for moving said work holder and said tool withV respect to one vanother into and out oi' a working range, almovable stop arranged to cooperate with said member to restrict movement oi said power means ina direction to move said tool and said holder toward said working range.

a movable stop arranged to cooperate with said power means to restrict the movement of said tool and said holder toward said working range, means including a cam arranged to aiord movement of said stop at a plurality of diierent speeds for determining the rate of movement of said tool and saidwork holder with respect to one another by operation of said power means within said working range, means for effecting simultaneous operation of said power means and of l said cam, means dependent upon a reduction of the work to a rst predetermined' size for reducing the rate oi movement of said cam, and means dependent upon a further reduction of the work to a second predetermined size for actuating said power means to move said tool and said -holder apart with respect to one another and out of said `working range.

6. An abrading machine comprising a work holder and an abrading tool which are relatively movable to feed the tool toward and away from the work, power means for effecting such relative movement, means including a longitudinally movable wedge-shaped cam and arranged to provide a stop for said-power means for determining the rate of movement of said tool toward the work,

and means dependent upon the reduction of the y work to a predetermined size for stopping the operation of said power means to move said tool toward the work, said cam being longitudinally movable through` a wide range to effect a relatively small movement of isaid tool toward the work whereby any further reduction of the -work caused by operation of said tool after initiation of the stopping of said power means will lie within a predetermined permissible working tolerance.

7. An abradng machine comprising a work holder and an abrading tool which are relatively movable in feed the tool toward and away from the work, power means for 'eiecting such relative movement, means including a longitudinally movable wedge-shaped cam and arranged to provide a stop for said power means for determining therate of movement of said tool toward the-work, means dependent upon the reduction oi the work/to a iirst predetermined size for reducing the rate of longitudinal movement of said cam, and means dependent upon the further reduction of the work to a second predeterl working tolerance.

means including a cam arranged tti-determine the y rate of movement of said stop when said` mem- 8. An abrading machine comprising'a work .holderand an abrading tool which are relatively movable to feed the tooltoward and away from the work, power means operable by fluid pressure for eiecting such relative movement, means including a cam and arrangedto provide a stop ber is moving-said tool and said holder toward 101' Said Pliwe'l'` means for determining the rate of movement of said tool toward the work, :duid pressureoperated means i'or actuating said cam,

means for supplying iiuid under pressure to said through a wide range to allord a relatively small movement of said tool toward the work whereby any further reduction of the work caused by operation of said tool after initiation ot the stopping of said power means will lie within a predetermined permissible working tolerance.

, 9. An abrading machine comprising a work holder and an abrading tool which are relatively movable to feed the tool toward and away from the work, power means for effecting such relative movement, means including a cam and arranged to provide a stop for said power means for determining the .rate of movement of said tool toward said work, fluid pressure operated means for operating said cam, means for supplying fluid under pressure to said means for actuating said cam, means -arranged to restrict the iiow of uid through said cam operating means for reducing the rate of movement 'of said cam, means dependent upon the reduction of the work to a iirst predetermined size for actuating said last mentioned means to reduce the rate of movement of said cam, and means dependent upon a further reduction of the work to a second predetermined size for stopping the operation of said power means to move said tool toward the work, said cam being movable through a wide range to afforda relatively small movement of said tool toward' the work whereby any further reduction of the work caused by operation of said tool after initiation of the stopping of said power means will lie within a predetermined permissible working tolerance.

10. An abrading machine comprising a work holder and an abrading tool which are relatively mo'vableto feed the tool toward and away from the work, power means operable by fluid pressure for eiecting such relative movement, means including a cam and arranged to provide a stop for determining the rate of movement-of said tool toward the work, means operable by uid pressure for actuating said cam, means for supplying fluid under pressure to said power means and to said means tor actuating said camfmeans arl rangedto restrict the iiow of uid in said means for actuating said cam for changing the speed of operation of said cam, means dependent upon the reduction of the work to aiirst predetermined size ffor actuating said last mentioned means to reduce the rate of movement of said cam, and means dependent upon the further rei-` duction of the work to a second predetermined sise for stopping the supply of uid under pressuretosaidpowermeansandtosaidcamactuating meansto stop the movement oi said tool toward the work, said cam being movable through a wide range toail'ord a relatively small movement of said tool toward the wo'rk whereby any reductionof the workbelow said second predetermined size caused by operation of said tool after initiation o! the stopping oi said iiuid sup-- ply means will lie within a predetermined permissible working tolerance.

11. An abrading machine comprising a work holder and an abrading tool which are relatively.

movable to feed the tool toward and, away from the work, pow'er means operable by iluid pressure .15.

for eiIectlng such relative movement, means including a cam arranged to provide a stop for said power means for determining the rate of movement of said tool toward the work, reversible means for supplying iluid under pressure to said power means, and means dependent upon reduction of the work to a predetermined size for actuating said last mentioned means to reverse the operation oi said power means and to move said tool away from the work, said cam being movable through a wide range to afford a relatively small movement of said tool toward the work whereby anyvfurther reduction of thework caused by operation of said tool after initiation of the reversing of said power means will lie within a predetermined permissible working tolerance.

i2. An abrading machine comprising a work holder and an abrading tool which are relatively movable to feed the tool toward and away from the work, power means ioreiecting such relative movement, means including a cam and arranged to provide a stop for said power means for determining the rate of movement of said tool toward said work, iluid pressure operated means for actuating said cam. means for supplying iluid under pressure to said pressure operated means for actuating said cam, means including a twoposition valve for controlling the rate of llow of iiuid through said cam actuating means for determining the rate of movement of said cam, means for initially positioning said valve to eiect a predetermined rate ot movement of said cam, means dependent upon the reduction of the work to a firstpredetermined size for positioning said valve to eiiect a reduced rate of movement ot said cam. and means dependent upon a lfurther reduction ci the work to a second predetermined size for stopping the operation of' said power means to move said tool toward the work. said cam being movable through a wide range to ati'ord a relatively small movement of said tool toward the work whereby any ilu'ther reduction of the work caused by operation oi said tool after initiation oi' the stopping oi said power means will lie within a predetermined permissible working tolerance. r 13. An abrading machine comprising a work holder and an abrading tool which are relatively movable to reed the tool toward and away from the work; power means including a power transmitting member and a fluid pressure motor for eiecting such 'relative movement, a stop arranged adjacent said power transmitting member and an abutmenton said member adapted to engage said swp for restricting. the movement of said member to move said tool toward the work, means including a cam arranged to aflord movement of said stop to determine the rate of movement ot said tool inward the work, a iiuid pressure motor for moving said cam, means including a valve operable in one position to supply duid under premura for forward movement of said motors and operable in another position to supply fluid under pressure tor the return movement of said motors, and means dependent upon the redliction of the work to a predetermined size for operating said valve to effect said return movement o! said motors, said cam being movable through a wide range to eil'ect a relatively small movement ot the tool toward the work whereby any further reduction of the work caused by operation of said tool after actuation of said valve toward its reversed position will lie within a predetermined le working tolerance.

114. An `abrading machine comprising a work* support and a Wheelv slide, an abrading wheel ro'- tatably mounted on said slide, means including a motor. operable byY uid pressure and a power transmitting member connecting said motor and 4 said slide for -moving 'said wheel toward and aw'ay from the work, a ymovable stop arranged strlcting the movement of said wheel toward the work, means including la cam having. an inclined surface for affording movement of said stop to to engage said power transmitting member for f restricting the movement of said wheel toward the work, means including a cam having an indetermine the rate of movement of said wheel toward the work, a motor operable by iluid pressure for moving said cam, means for supplying' fluid underpressure simultaneously to both of 4said motors, means including a valve for reversclined surfacevfor affording .movement of said wheel toward the work; a motor operable byfiuid stop to determine the rate of movement of. said l pressure for moving said cam, means for supply ing iiuid'un'der pressure simultaneously to both oi said motors, means including 'a valve forl re f versing the direction of fluid flow to said motors-v for reversing said motors, and means including a. gauge arranged to determine the size of the Work and dependent upon the lreduction of theworkv to a predetermined size for actuating Asaid valve to reverse said motors.

i5. An' abrading machine comprising a work supportand a wheel slide, an abrading wheel rotatablymounted on said slide,'means including a motor operable by fluid pressure and a-power transmitting member connecting said motor and said .slide for moving said wheel toward and away from the" work, a movable stop arranged to en ing the direction of fluid flow to said motors to reverse said motors, a control valve operable in one position to aii'ord a relatively free flow of fluid through said cam, ,operating motor and operable to a second position to restrict the flow of fluid through said cam operating motor for varying the rate of movement of said tool toward the work, gauging means dependentl upon thereduc tion'the work to a predetermined size for actuatingsaid valve to its second position, and means .dependent upon a further reduction of the work to a second predetermined size for 4actuating said motor reversing valve to move said tool away from the work, the inclination of said cam being such'th'at any further reduction of the work'by operation of said tool afterinitiation'of the operation of said 'reversing valvewill lie within 'a predetermined permls'sibleworking tolerance'.l

CHARLES J. As'rRowsKI.

gage said powertransmitting member for 're.

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